Bad memory
You probably have failing memory sticks. I had the same issue when I purchased "value ram"; it lasted for a month and then my games started crashing...I could not install anything, and blue screen lockups started.
Google Memtest86 and download the software. Follow the directions by rebooting and running it before Windows starts (in the bios). If alot of red errors come up...I bet they will, you have chips that are bad.
