but it depends what your processor is doing at the time. If you're running graphic intensive applications etc, it may run hotter.

A system that keeps re-starting could be caused by over-heating. Have you cleaned the fans of dust? What happens when you run the computer with the case open to allow more airflow?

Also, check your capacitors. Do they look bulged, or are they leaking?
http://www.pcstats.com/articleview.cfm?articleID=195

Mark