After booting and when i start to work on my PC, suddenly the monitor goes black but the pc does not hang. Sometimes, during boot up itself, after the windows xp loading screen goes, it becomes black. If i force shutdown and restart again, windows gives me a error saying" Windows did not start properly, this may be due to a recent hardware or software change....." and Gives me options like Safe Mode, Last Know.... and Start Normally. Please help me! I checked for bad sectors, but it reported none.