Unexpected shutdown windows

I had xp. In xp i was facing unexpected shutdown error(blue screen).It says Memmory_Management. Even i uninstalled and installed win 7 i am experiencing same prob. It happens regularly in about 15-25-30 minutes sometimes fast also 1 inute or even on startup. I checked POWER OPTION also. My friend suggest me to change Fan And The circuit on which proccessor is. What is the Fix?