Thanks for your input guys. I need some more now though.

This system has been apparently restarting all by itself every now and again. It use to do this before. Then the cpu fan went out and the entire machine wouldn't even start. After replacing the cpu fan its up and running again.

However I will leave and come back and half the time the white desktop saying 'active desktop has been disabled' etc is on the monitor. Which indicates to me the machine restarted itself at some point. There are no apps running except Sygate Personal Firewall and perhaps the Opera web browser. Nothing that I am aware of that would cause the machine to restart by itself.

It was suggested to me when systems begin to overheat they will reboot themselves.

When I replaced the cpu fan I had accidently removed the heatsink. So upon replacing the heatsink I cleaned off the old thermal goop and followed the instructions in applying some new thermal goop and did the best I could to apply it evenly.

the new cpu fan and all fans inside the system seem to be running well. I downloaded a cpu monitor called 'sensor view' to keep an eye on cpu temp etc. It's running around 106 - 108 degrees farenheit.

There a fan called the sys fan that the bios and the monitor say isn't running. There are only 3 fans in my tower that I see and all 3 are running. The fan inside the PS. The cpu fan, and the fan attached to the tower that blows the heat out of the tower.

Anyone have any ideas?