This sounds a lot like a memory problem. Use either of the following to test your computer memory. Let it complete at least 3 passes. Running overnight is even better.
There are two programs that are normally used to test computer memory, Memtest86+ and Microsoft Memory Diagnostic. They are available from the following locations: Memtest86+ Microsoft Memory Diagnostic
They are bootable CD ISO images. You don't burn the iso file itself to CD., you create a CD from the iso file using your CD burning software. There is a good freeware burner called ImgBurn
which will do this easily.