Every now and then my computer freezes completely, nothing works at all and I have to switch off and back on again when I get the message "Your computer did not switch off properly etc" I have windows vista running and it is most annoying. Any ideas anyone?
Also check that the fan is running properly and that all of your computer's ventilation slots are unobstructed. (Overheating is a common cause of computer lock-ups).
A possibility is security software. Norton Internet Security used to completely freeze my machine for at least 15 seconds at a time, and could do that several times in quick succession. It didn't stay on my computer for too long after that started happening.