Did you run memtest? You can also run Windows Memory Diag if you have Windows 7? That will let you determine if you're looking at a memory problem, though with memory problems, they seem to occur more than 1-3 times a month. You'd be seeing things 1-3 times+ every time you try to use it if you have bad memory.
First thing I thought when I read your post was power supply. But try the memory checks and let us know.