Desktop

Your description is not clear so am assuming that PC runs for awhile and then shuts down. Can't power back up until about an hour later.

Sure sounds like a heat related problem. Two most likely components to overheat are CPU and power supply. High end video cards are another.

Check CPU cooler to ensure fan is operable and that cooling fins are not blocked. Would be a good idea to remove and clean and apply new thermal compound.

Check power supply cooling fan(s) for blockage. Also check air intake vents.

Another common cause of overheating is blocked case air intakes. Ensure that air vents do not have dust buildup blocking them.

Clean fans, CPU cooler, and air vents with canned air as needed.

Dalton

I agree with Dalton, it's a heat issue.

If you have added aftermarket graphics and sound cards you MAy find you need and extra fan onboard.

YOu can pick up additional fans at local elexctronics stores, or PC retailers, they are pretty cheep and a computer can never have TOO much air circulation.

If you hear fan NOISE it could be a dry bearing, you can relbe them with a siongle drop of machine oil b=underneath the center sticker, but it's usually best to drop a few bucks and replace it, they are pretty cheap.

to get a new SMPS ,
n tat to higher powered SMPS

you said you added another (HDD?) drive and a cd burner......
Your original power supply is prob only round 300 watt or less - I'd say a 450 watt PS will solve your probs but also as stated by other posters, checking fans and cleaning helps to keep good air flow .....