Put your old hardware back in first. Does it work? If yes, then run this:
http://www.guru3d.com/files-details/display-driver-uninstaller-download.htmlRemove any drivers, shut off the computer, swap parts and try again.
If that doesn't work then you'll have to repair the Windows installation. Without messing with command prompt, you can usually get away with a system restore from a Windows installation disc/thumb drive. If you need an installation disc, I'd suggest torrenting one, preferably a MSFL version. That will be a pure install, straight from Microsoft. There's no problem downloading it. It's only illegal if you install it with an already used serial key or bypass the activation. You're just using it for repair.
I'd almost wager that the issue lies in the memory you swapped over. Perhaps the timing/speed is different between the two computers. Resetting the BIOS might fix it but in some cases not, it may not be running at the speed/timing/voltage it needs to. I've personally swapped Nvidia graphics cards in and out of different models and didn't have an issue. The "proper" way is to clean the old drivers out first and do a clean install on the new drivers from Nvidia, not the manufacturer.