I had the same problem but with the spike-guard, so i plugged the computer directly into the wall socket and the reboots stopped. Your temperatures are a little on the higher side if you have an original Intel. Also, running TurboC doesn't put your system on full load, it just appears to be doing so. You should try running a resource hogging game or maybe convert a few movies from one format to the other to really test your system.
So I am in a dilemma whether the problem is with the cooler or the UPS.