On buying/building a PC...
The biggest thing about buying or building a PC is RESEARCH. Start with what you want to use the PC for most of the time & what its hardest task will be, & then compare CPU reviews. 2nd, find out how important the amount of RAM is to what you want to do. Often enough the hype that more RAM is always better is just that, hype, especially if you do the same things over & over where you might get more benefit per dollar spent from Intel's tech using a smaller SSD for caching -- most [90% +] of my software works as fast in XP Pro 32 as it does in win7 64, where the available memory more than doubles. 3rd, do you need an add-on graphics card, or 2 - 4 of them? On-board graphics have gotten quite a bit better, & if the PC isn't going to be used for gaming that might well be all you need. 4th, how many add-on cards do you want/need to use? On-board audio can be quite good for example, but it doesn't always cost that much to do better by adding a sound card. Once you've answered questions 3 & 4 you know how small your new PC can be -- while there are some really tiny setups [the PC equivalent of a netbook], motherboards mostly come in 2 sizes, ATX & mini ATX, with the mini version limiting add-ons simply because there's less room, no place to put them on the smaller board... smaller boards & cases cost less. Now you can start comparison shopping.
In the next paragraph I talk a little bit about pre-built PC & kits, but I think really the deciding factor is more often along the lines of can I build one & do I want to bother? Some people like to build their own for the same reasons some people like to tinker with their cars, & while they're often the loudest voices, this DIY crew I think often doesn't pay much attention to the purely practical stuff, like answering those 2, very basic questions. My take is this... IF you re-use some of the stuff you've already got, you can very often save money building your own. IF you want/need something higher end you can save money, IF you shop wisely & carefully. IF you want a complete, out the door PC with very average to lower end specs, IF you watch for a good sale price a pre-built PC is very often cheaper. Can you do it & is any money saved worth it? That part only you can decide. If you save $100 & the time it took would have otherwise been spent watching TV, that's very different from someone with little to no free time who gave up a chance to make $200 so they could assemble the parts. If you go fast & don't have problems you could have the mechanical end of things done in less than 1/2 an hour -- if you go careful & slow, routing cables behind the m/board panel [when/if the case allows it], tying all the cables up etc., you might spend a couple of hours. On top of that you have however long it takes to set up Windows & whatever software, & if you want to overclock [make the electronics run faster than out of the box], you might spend a couple weeks on that portion alone, test -> tweak -> repeat. At any rate to help folks answer those questions for themselves, can I & should I, I try to point out a few pros & cons going the DIY or the pre-built route. 2nd I list the basic parts, ignoring stuff like the keyboard, mouse, & monitor that you'll also need. I also include just a little about what to look for. 4th & 5th I talk a little about motherboards & graphics cards, & 6th, try to give a brief overview of how everything comes together.
It's cheaper to buy in bulk, so companies that make/sell PCs pay less for the parts than you will. The tradeoff is that individual components may be lower quality than what you might buy, & expansion is usually limited, meaning adding or upgrading hardware will probably be easier, or may only be possible with a custom built PC. On the flip side, however frustrating their tech &/or customer support may be, you're dealing with one company instead of several -- with a custom built PC there's the manufacturer, possibly their supplier, & the seller to deal with, for each part. You might also want/need to figure in the cost of Windows -- a fresh copy will definitely cost you more than a company like HP or Dell pays. As far as transferring a license from an existing PC, your options may be severely, legally limited [if that matters to you]. Somewhere in between, many companies sell kits, which are simply bundles of parts sold as a reduced price package deal -- if you buy one of these bundles you're more certain the parts will at least work together, & it might make resolving any problems easier... on the downside the seller may be packing whatever bundle with stuff that hasn't been selling well, & when something doesn't sell well there's often a very good reason.
To put a PC together at minimum you'll need a Power Supply, Case, Fans, Hard & Optical Drives, Motherboard, CPU & Heatsink. Cases vary considerably in quality & price, but with no moving parts, & only a couple switches & plugs to break or wear out, as long as the design has adequate airflow, one's generally as good as another for the average consumer. If you plan on heavy duty over clocking &/or 2 - 4 high temp graphics cards then airflow becomes much more important, as does the case dimensions since you'll need to either fit water cooling or often a taller CPU heat sink. You might see hype about tool-less drive &/or card slots, but unless you're planning on changing those often, who cares? The case simply holds all the other parts & may or may not make a fashion statement. The fans that go inside the case may come with the case [usually you get some but have spaces to add more], & they too can vary in quality & price -- here you want to look for failure rate & noise levels, plus more expensive fans can have their speed [& thus noise levels] controlled by the motherboard [if this is important to you make sure to look at how many fan plugs are on the motherboard you're thinking of buying]. Regarding Power Supplies, I'll Scream RESEARCH... it's unfortunately not uncommon to find sub-standard & even Fake electronics inside! It used to be you could go by weight if nothing else, but they've taken to adding rocks & cement. Further muddying the waters, many [most?] major companies don't design or make the power supplies they sell, so a model sourced from one factory may be entirely different from another model built elsewhere. Look more for pro reviews where they've actually measured output etc. rather than relying on anonymous user comments that it worked, though obviously a reported high DOA rate is useful. Power supplies come in different wattage ratings -- how much you need is usually determined mostly by the graphics card(s) you'll run -- there are several sites with calculators where you plug in your choice of hardware & they'll give you their recommended wattage rating. Personally I like modular supplies, where you don't plug in the cables you don't need, & that reduces clutter, but as they're mounting the power supplies on the bottom of the case more & more often that becomes less important [the cables sit on the floor rather than hanging from the ceiling].
On motherboards... I was cured of being an early adopter by a new board that briefly caught fire. Now I only look at motherboards that have been in the field ~6 months. That also BTW makes them [sometimes Much] cheaper, & gives the manufacturer time to update the firmware [Bios] to fix all the bugs -- it gets old, fast, when you find yourself checking for Bios updates weekly or even daily, hoping to get your PC *finally* working properly. You start by picking out the CPU you want to run, plus a 2nd [& maybe a 3rd] choice, then choose the preferred chipsets you want on a motherboard compatible with that CPU -- AMD & Intel typically have ~3 - 4 chipsets they sell to motherboard manufacturers, & you compare them based on reviews & the selling price for the m/boards. Then once you have a chipset in mind you can start reading customer reports & reviews of different m/board brands/models. However it's hard to catch everything, since reviewers test a board rather than live with it, customers generally write comments or reviews when the product they bought is still new, & common problems may not get mentioned because the author figured everyone knows that already -- it was only after the fact that we found two different m/boards we bought this year each had a different problem chip incorporated into their design [1 was for USB 3.0 & 1 for SATA III]. Because of their other features & the sale pricing I can't say we wouldn't have bought them had we known, but it would have been nice to know beforehand -- I guess if you want to be really safe Google/Bing the individual add-on chips the same way you research the board they're on. If you're not going to over clock you can often get by with a cheaper m/board -- if you are interested in O/Clocking you'll often find your best choices include features like extra graphics card slots you may not want/need. You'll likely find the fancier m/boards get a Lot more press -- Do Not assume that cheaper models are going to equal their higher priced siblings... you may *see* a smaller [or no] heat sink, but miss other places they cut costs, e.g. using a trouble prone Bios. Even though you probably already know this, I think it bears repeating -- people that are fans of a company or brand are biased, & most people that have just spent a bunch of money want to feel they did so wisely... take whatever they say with a grain of salt. If I'm in the manufacturer's or whatever forum I look for posts from new people rather than old timers when I'm trying to gauge a product's quality -- when I read customer comments/reviews I start with those that rated whatever the poorest.
On graphics cards... If you're a gamer read up on what works best with the game(s) you play. Running 2 - 4 cards *may* make use of all your cards, or it may turn out to be a needless PITA. You may be better off running one top of the line card, or one or more mid-range models. ATI might work best with game *X*, while Nvidia scores with game *Y*, & with game *Z* it's a toss up. I don't think taking a more fan-based approach, researching a particular graphics card/chip itself is that effective -- see what others playing your favorite games & running those cards have to say. If you work with video like I do, you might find [like I have] that Virtu is Very important, perhaps more important than what graphics card you run -- Virtu uses the graphics portion of an i7 along with your add-on graphics card, in ways that are not always documented or expected, & it can be very, Very fast. Whatever brand you use, I suggest giving the MSI Afterburner software a look.
Assembling a PC is not terribly difficult, but if you tend to be a klutz or if the 1st tool you reach for is always a hammer, you might want to have someone else put it together or buy pre-built. When handling the electronics parts Always ground yourself, watch out for static electricity buildup, maybe wear a connected grounding bracelet etc. You start by snapping the rear access bezel into place in the case -- it comes with the m/board -- then screw in spacers called Stand-offs to match the m/board's mounting holes. If your CPU heatsink or water cooling block uses a special mount, add that to the m/board -- if your case has little space to work in you might add the CPU & heat sink as well. It can also be helpful to add the RAM beforehand, depending on where the m/board's mounting holes are & the size of the RAM stick's heatsinks -- it's easier with the m/board out of the case, but you have to be able to put the screws in place. Depending on your case design, it may be easier to mount your drives &/or at least some of the case fans before adding the m/board. The power supply's held in place by 4 screws that go from the outside rear of the case into the power supply -- also depending on case design it may be easier or necessary to add the power supply before you add the m/board, or the CPU heatsink, or leaving it out for now may give you extra room for your hands. Adding the m/board itself can be a bit tricky because that bezel I mentioned can have parts that press against the m/board's rear plugs to ensure a good ground -- you might have to angle the board a bit to fit underneath an arm or 2, & you will most likely have to lightly press the board against the bezel to get the mounting holes to line up with the stand-offs, all while taking care that those same stand-offs don't cause any damage to the backside of the board while you're moving it around. Holding it in place with one hand, I use the other to start one screw, then start the rest before tightening them all -- I usually start at one end & work towards the other, but I haven't read anything that says to do it that way or use a cross tightning sequence etc. Once the m/board, power supply, CPU & heatsink, RAM, drives, & fans, are in place you can start plugging everything in -- the m/board gets 2 or 3 connections from the power supply, all drives get connected to the power supply, fans get connected to the power supply or the motherboard, and any wiring from the case for switches etc. get's plugged into the m/board as well. It can be better to hold off adding any cards, including graphics cards when/if your m/board [&/or CPU] have on-board graphics -- it's simply less to troubleshoot if the system won't boot -- but there's no reason you can't add any cards before or after you start plugging in all the wiring. Higher end graphics cards take 2 wires/connectors from the power supply. The [normally] SATA cables connecting your drives to the m/board can be skipped initially -- the sockets where the cables plug into the m/board often fit the cable ends a bit sloppily, so there's always the possibility you'll bump one of these rather stiff cables, cause it to disconnect, & then have to go back checking why a drive is missing. I usually boot to USB stick the 1st time anyway, so I avoid as possible plugging in any SATA cables until I'm done poking my hands around inside the case. When the minimum's hooked up, including a mouse & keyboard, just follow the m/board manual, starting the PC & going to the Bios for initial settings -- once you get everything going you'll likely want to revisit the Bios for additional tweaking anyway, so you may want to just set the Bios to load & use it's default settings [often a hot key]. Make sure everything works 1st, then go back & make it work better.
