I have recently purchased a Sony VAIO with Windows 7 pre-installed. Completely randomly (this happens more often now - every 30 mins or so) the computer will freeze up, then brings me to a blue screen telling me that "A problem has been detected and your computer has been shut down to prevent damage". This stays on for only a second then the screen goes black. Five seconds later I get "Operating System Not Found". The only way I can use the computer again is to hold the power button down (which gives the computer a full power off), then turn it back on again.