Could I have some PC specs please. Preferably OS, Service Pack (if Windows), Graphics card, Processor, RAM & Power Pack. Also have you made any hardware changes recently and is it a Lappy, or desktop? Any unusual environmental heat (hot day), or PC getting unusually hot? Have you cleaned the poota out recently? How long have you have the current processor without reapplying coolant?
Oh and can you hear any sound in the background when your monitor falls over?