That CPU temp is fine, I doubt that is your problem.
Do you have up to date Antivirus protection? Have you checked your system for virii, or spyware recently? Some virii lately will make your machine reboot. You might take a look in the Security forum, and read the following topic:
http://www.daniweb.com/techtalkforums/thread5690.html
Another thing: Have you installed anything new lately? Like new software? Windows XP Service Pack 2? (Read this if you just installed SP2 and started having this problem:
http://www.daniweb.com/techtalkforums/thread10031.html).
If you're sure you have current virus protection, and aren't infected with something, or loaded with spyware, you might consider checking all your cards and connectors inside the case, (Video cards, sound cards, modems, memory, hard disk cables, etc), to be sure nothing has worked loose, as that can cause intermittant reboots, especially as the PC heats up and parts expand. (I usually actually remove the cards and hard disk cables from the slots, then reinsert them to insure I'm getting good connections).
Hope some of this helps.
Unsolved 
