hello, I had the same problem some time ago, not exactly sure how I fixed it but I know the feeling of having a dodgy comp.
Have you overclocked the CPU (If you have no idea what I'm on about then probably not!!) if so just slow it down a bit, a slow comp is better than no comp.
Have you recently installed some new hardware, I think mine may have been a conflicting graphics card, If your confident remove the graphics card and try onboard graphics only.
And finally... is your copy of windows real? I had a dodgy copy and it was full of bugs, corrupt files etc etc
Good luck