Yellow Screens / Monitor Disconnects

Hi. I just built this gaming computer in september. It was running mostly smoothly, but about 2-3 weeks ago I began having trouble running some of my games. Let me give you my specs real fast

4 gb of ddr2 ram
Nvdia Geforce GTX460
AMD phenomenon II x4 955 3.21gherz processor
790XT A-UD4 motherboard by Gigabyte.

Now, It started with Fallout. I was playing Fallout New Vegas and all of a sudden the skybox and certain objects will turn a solid yellow, and then right after that, I will get the "Fallout.exe has encountered and error and needs to close." but my resolution will go to 600x800 and then the monitor will just shut off. The computer is still running, but the monitor is not connecting to the computer. The only solution I can find is to restart, but I cant play fallout or it will happen again.

Recently its began spreading to my other games as well. Randomly, my computer will BSOD at times and restart. I am for sure this is not a virus because Ive scanned my computer with about 3 different programs to check. (Avira AV, MalwareBytes, Spybot SD)

Any help on this would be greatly appreciated, because im truly at a loss.