The following is/was an attempt to help someone who asked a question in the comments. To me it was also an interesting question to think about. There may be something there that gives someone an idea or 3, or it may be useless trivia, but if it helps out one person someday, well then it's worth it IMHO.
#4: “Will this software allow you to recover a program which was accidently uninstalled and all registry keys pertaining to that program removed? No other action (other than booting and shutting down some dozen times or so) has been taken.”
TO answer your question directly, the odds are against it — the registry is constantly being altered, so the odds are very high that portions of the registry files with removed/deleted keys have been overwritten. Add to that, the registry is a set of files making it more complicated, and you need to know what you’re looking for inside the registry, if you were successful in recovering an old copy & can open it in something like Regedit. For the following I’m assuming you no longer have the key or number you used to register &/or activate the software — if you have that you could simply reinstall the same version, or using something like Time Freeze, try registering a different version.
Few programs remove all of their registry keys & values when uninstalled, so it can be worth a shot to try and recover the program files themselves, or to simply install a trial or unregistered version of the software — registration data, if stored in the registry, might still be there & work. There’s also the chance however that a new installation will overwrite any registration data left behind, whether that data’s stored in the registry or elsewhere.
How much trouble you go to is up to you, & depends on how badly you want the software back, but ideally you would make a complete clone of the partition, *including free space*, using a bootable CD/DVD/USB stick. The more you run your installed copy of Windows the greater the chances that lost data will be overwritten. Then you can later work with recovering files from that clone if necessary.
Because registration data can be overwritten, it might work to get a copy of the program’s folder. I would install the same version to a VM [Virtual Machine] & copy the program’s folder from the VM — or I could use something like Time Freeze, install the software, copy the program’s folder elsewhere, restore Windows [with Wondershare Time Freeze that means a re-boot -- other virtualization software may work differently], then copy that program’s folder back into place. An easier way is to use 7-Zip or Universal Extractor to get the program’s folder out of the setup file, but that does not always work.
Then with the program folder in place, I would try running the software, again using Time Freeze because I don’t want any chance the registration key might be overwritten. If it doesn’t work that way, & doesn’t work installing the software, then I’d try recovering the program’s folder & any other files & folders it used — if you tried [or try] installing a copy of the software you can find out what files & folders it adds outside of the program’s folder, so you have a good idea what you’re looking for. Bear in mind that registration data may be stored in one or a few files, so you don’t necessarily have to be successful recovering everything — it can work to get what you can, then copy that into the software’s folders after copying the folder(s) into place or a reinstall as above, overwriting what’s there.
If all that failed & you want to tackle looking for old registry files, backup the existing registry with ERUNT, which will show you just what files you’re looking for. If you can recover a copy or copies of those files, you can try opening them in Regedit or similar to look for whatever keys & values. You can also make a copy of the ERUNT backup folder with a different name, or just re-run ERUNT storing the results in a different folder. Then replace the files in one of those folders with the files you’ve recovered, & run the copy of ERUNT in that folder, which will replace your existing registry with the recovered files. It may or may not work, & Windows may or may not start afterwards. As or if necessary, to put things back the way they were, run ERUNT from the 2nd, untouched folder, after booting with whatever rescue disc or booting to Windows repair/recovery environment command prompt. Needless to say a full partition image backup before you tried something like that would be a Very good idea.
Best Luck
* * *
#9: "One thing cannot be recovered and this is your registry. Your registry is not deleted! It has changed values in the registry. In this case also your “registering” and program details. You cannot recover these information with any program, since this is a permanently ongoing dynamic process."
In C:\Windows\System32\config\ & C:\Users\[UserName]\ you'll see copies with the file extension .BAK. Copies of the registry I think are made occasionally. I don't know if any usable registry files would show up running a file recovery app, but if they did, replacing the existing files with those or the ones with the .BAK extension using ERUNT may or may not work. Mounting them in Regedit or similar, assuming you had an idea what to look for, may or may not work. But if you can put things back [have a backup & know how to restore it], if you're desperate enough it might be worth a try.
Personally I've had mixed results with that sort of thing, & I've never tried it to recover registry data from a Windows install that had software removed & then was run for however long. Another thing I've done that **might** work in this case is installed a copy of whatever software in a VM, tracking everything, then compared those registry entries to what I had in my regular copy of Windows. That showed me what entries I needed in regular Windows registry, & showed me what changed values in regular Windows registry might be exported & later merged after a new installation of the software.
Likewise a monitored install in a VM shows me what other files/folders are involved, so I could look for them in my regular copy of Windows. Very often registration data is stored in a file rather than the registry. Myself I'd mount a backup archive & look for those files as necessary, but I'd run recovery software looking for them if I didn't have the backup.
However, that all said, I've never attempted what George is asking about. I've had problems transferring software from XP Pro to win7/8.1, some of it dating back to win98, & that's sometimes taken quite a bit of detective work. I also do quite a lot sometimes to avoid or work around troublesome install routines, using my VMs.
