cookie10,
It sounds like you may have a heating problem. Take a close look at all the vents on the system, make sure they are free of dust bunnies. A can of air from the local office supply place will help, blow everything out well.
Make sure there is adequate air flow to the machine while running. If there are little swing down feet on the bottom of the unit, use them. A laptop cooler mat may also be helpful.
-Fred