Could be a RAM fault, if you have more than one stick, try removing one at a time to see if fault goes.
Check your disk for errors.. Start, type cmd, Right Click on Cmd prompt and 'Run as Administrator'. Type chkdsk /f /r then Enter. (note spaces before /). Type Y and Enter to run the program when you restart Windows. Expect it to take a long time if you have a large drive. Use this to check out the chkdsk log http://www.sevenforums.com/tutoria
If nothing obvious found and fault continues consider Re-install/ Repair Install of