A few notes:
If you go to Toshiba for service there's a good chance that, like other manufacturers, they'll put everything back the way it came out of the box. You might be able to do that yourself, depending on what Toshiba included [on the hard drive &/or CDs/DVDs] when you bought it, though either way you'll loose anything you've installed since then.
Something else I wanted to mention, in researching your notebook I saw it might have come with the WinDVD player. Is it possible that that player updated itself? Personally I've never been able to get the WinDVD player working on this system using ATI graphics.
I have seen & read of problems with the AMD/ATI Fuel service, which is used for overclocking but installed by default -- you can try stopping it with Task Mgr or in Control Panel -> Administrative Tools -> Services *if* it's on your laptop & running.
For full screen video in your web browser you can *try* right-clicking any Flash opbect or component on I think any web page, & turn off graphics acceleration from the pop-up menu.
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On the ATI graphics stuff please bear with me as this gets complicated...
There doesn't seem to be an awful lot of info available, but from what I can tell Toshiba has less common [higher end] laptops with dual graphics -- the AMD/ATI versions use something ATI calls Enduro, which is a technology to switch between the two graphics processors. The HD 6620G is part of the main processor [CPU], while the HD 7450M is separate with it's own dedicated RAM, though it can still share the laptop's regular memory. The HD 7450M uses more power than the HD 6620G, which hurts battery life, so the laptop is supposed to switch between them, for example I found one reference that said the HD 7450M will only operate if the Toshiba laptop is running on AC power. Many laptops let you switch between the 2 graphics processors yourself, either with a hot key combo, or maybe right-clicking on the desktop & making a selection from the pop-up context menu -- however whether you can do that switch yourself or not depends on the laptop manufacturer, & I didn't see any info re: Toshiba, nor did I see anything in the PDF manual I read.
Both graphics processors have video playback/encoding acceleration, but the HD 7450M has more, is more powerful in that regard. I didn't see much info on the HD 7450M itself in the way of reviews or specifics, only the HD 7xxxM series as a whole or concerning the flagship HD 7970M [ http://www.amd.com/us/products/notebook/graphics/7000m/7400m/Pages/radeon-7400m.aspx#1 & http://www.notebookcheck.net/AMD-Radeon-HD-7450M.57211.0.html ]. Most of the complaints I saw for the HD 7xxxM series using Enduro had/have to do with more demanding games.
From what I've read Toshiba laptops will only let you use or update drivers released by Toshiba, though I also read that ATI Beta drivers don't have or enforce that limitation. The Toshiba site [ http://www.mytoshiba.co.nz/support/download ] requires a product number [e.g. PSK4UA-00K001 is the 1st choice] so I don't know how recent Toshiba's ATI drivers are for your specific model -- the Satellite drivers I had looked at were based on lower-end models with just the HD 6xxxG. The ATI drivers for the HD7xxxM graphics processors are the same as for their regular graphics cards. Right now there are 2 *Official* ATI Beta driver sets, + 1 unofficial beta that I'm aware of -- 12.6 & 12.7 here http://support.amd.com/us/Pages/AMDSupportHub.aspx & a later, leaked version here: http://www.mediafire.com/?1i1dja7mez7xb3a . Allegedly new drivers are due from ATI next week. From all the reports I've read they're finally starting to get all the kinks worked out for the 7xxx series, but, when I tried the latest *official* Beta drivers on my year old HD 6870, the video end of things was broken... the leaked driver fixed that, put things back to normal. I haven't read, don't know if the driver due next week is another beta or a regular version, & do not know if it's true that only a beta version will install.
So... I'd suggest 1st making sure your laptop was plugged in [in case the HD 7450M was disabled on battery power], see if you could manually switch to the HD 7970M [maybe the docs/manuals that came with the laptop have directions or try the right click on the desktop?]. You could also check that the display resolution hasn't been set too high -- I couldn't find info on *your* L750D, but the ones I did find info for list the max rez at 1366x768 . Regular ATI drivers include the Catalyst Control Center, which is where you'd set the display resolution -- you'd open it by right clicking the desktop or via its icon in the System tray area. If that didn't work you could see what Toshiba had for drivers/updates. Particularly if the files inside the self-extracting download aren't dated in the last couple of months [7zip expanded the drivers I downloaded] I'd consider the update that AMD/ATI is supposed to release next week or the leaked Beta -- again *allegedly*, ATI has been working on Enduro issues so the newer it is the better it may work. My thinking is that if the drivers got screwed up then re-installing should hopefully fix it, & if you're installing drivers might as well use the latest. If you do update the graphics drivers DO back up 1st -- it's very hard if not impossible to go back to the way things were otherwise if something doesn't work.
If you do install newer drivers, you will have a "ATI Technologies" folder in Program Files\Common Files [& Program Files (x86)\Common Files if 64 bit Windows] -- inside that folder are the files ATI drivers use for video playback/encoding. *VERY* often, on multiple PCs, I've seen driver installs/updates skip one or more of those files. I've also seen problems when the versions of those files was different from the drivers installed. You can usually tell at a glance if all the files are dated for the month of the driver release. Here's what I do, though if things work OK after updating the drivers you may not want to bother... The driver setup files include a ... \Packages\Apps folder -- it may be in a C:\AMD or ATI folder if you use the download from AMD.com. Looking in that Apps folder you'll see folders like WMVDecoder that hold an .msi file. I use Universal Extractor [ http://legroom.net/software/uniextract/ ] to expand those .msi files, then compare them to what's installed in the Common Files folders. If those files weren't updated, after stopping CCC & MOM in Task Mgr., I'll try running the .msi file & if that doesn't work, just drag/drop the files in place, over-writing the older versions. Note that if files are missing you don't want to just drag/drop since the files will have to be registered in their new location to work. Note also that for 64 bit Windows, Program Files is for 64 bit files, & Program Files (x86) is for 32 bit -- when you expand the .msi files you'll see that ATI stores 64 bit files in folders that are named to include 64. Note that I've had very long-standing issues myself installing ATI's OpenCL, which is one of those Packages\Apps -- I have to remove the install records using the "Windows Install Clean Up" app, then run the .msi file.
It get's more confusing... ATI used to call their video playback acceleration Avivo, & it's still listed that way in some places. If you go to download it from AMD.com it's listed as AMD Media Codec Package under Options. Sometimes the files or packages inside the Avivo setup files are all or partly included in the regular driver package -- sometimes not. *IF* you go to the trouble of checking & matching the files in the regular setup files, & if there's something missing, it's probably included in the Avivo setup package. And just like the regular driver package it may or may not update the included files. Note that while a package may be labeled WMVDecoder, that does not mean that's the only thing it does, or is needed for. In fact, traditionally disabling .wmv acceleration in Windows Media Player disabled it somewhere else too -- same with disabling graphics hardware acceleration in PowerDVD (?).
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AS far as 64 bit win7 goes, *If* you wanted to pursue it, I did come across posts where people wiped their Toshiba Satellite hard drives & installed win7 64... You'd have the issue of losing anything you'd installed, + the issue of needing to find 64 bit drivers for everything 1st -- that shouldn't be a big problem IF the ATI drivers from AMD.com work, but if you have to use Toshiba's, & if they only come 32 bit, it would likely be a deal breaker. There's also the issue of any Toshiba installed software, & *possibly* win7 activation. Don't know whether it'd be worth it... there are few 64 bit apps/games, & most video stuff is 32 bit, even in win7 64. Maybe you could take the extra RAM Windows wasn't using & set it to be used by the HD 7450M?
