run windows memory diagnostics. In start > search box, type memory, the first option will be windows memory diagnostics. Run it. it will restart the machine and after finishing the test the results will be in event viewer.
run HDTUNE and check harddrive for errors. What about other o/s ? You can try installing windows vista or windows xp and check . Could be a driver issue. For how long have you been using windows 7 sp1 on your PC ?. Have you experience these issues with other o/ses before ?. Stating your pc specifications will be of some help to give a solution ....