Windows error on installation

[ruit7]

The root of my problem started yesterday when I bought new RAM. I previously had two sticks of 512 MB in my 775-DualVSTA, and I bought a new 2GB stick. My motherboard says that I can run DDR2 @ 667 mhz, which this stick happens to be. I am not sure if the stick are DIMM or not.

I installed the sticks and turned on my computer and everything worked perfectly.... at first. My computer turned on MUCH faster and my programs ran a lot more smoothly. I tried to install Fallout 3, and about a quarter way through the installation my computer kept restarting.

I thought I needed a driver update of some sort so I went to Windows Update. In Windows Update, I saw I need two Hardware Drivers - one was for my monitor a B70D Hyundai to run on my video card - NVIDIA GeForce 7900 GTX. I installed both and restarted my computer. When my computer restarted everything was completely messed up. My computer couldnt switch out of 600 x 600 and run at 16 colors. When I tried to use any webbrowser, the browser crashed. Whenver I turned on my computer the screen would turn off for a second and then turn on. It did not matter if I uninstalled the monitor driver, it would be back if I restarted my computer. I got the newest video card drivers and that did nothing. I was not using any drivers by Hyundai before the update, I believed I was using "Plug and Play".

I used a restore point from a week ago, and this did nothing. I used another one from two weeks ago, and Windows wouldn't load after that. A blank green screen would just come on and nothing would happen. The desktop and taskbar wouldn't load. I tried to reinstall windows and I got error 426, and says my singnature code for Windows XP was invalid. I put my OLD RAM back in - same problem. I think I am just going to have to erase my C drive and start completly over again, but I think I still might have problems. As of right now - I cannot reinstall Windows OR repair it.

Does anyone know what might be wrong? I am 99% sure it's not the RAM, because everything was working perfectly before the Windows Update, and my motherboard says I can use DDR2 @ 667 mhz, on top of that - I encountered the same problems with my other sticks of RAM. I am using an intel E6600 dual core - if that matters.

Thanks!