Gateway LX6810 BIOS and fan issues. Help!

[Mountain Mike]

I have the GT5628 and the fan speeds up at random intervals then reboots. Sometimes the fan speeds up while I shut the computer down, and then does not completely shut down (ie it freezes up during shutdown). I have even replaced the motherboard. I blow dust out of it and the power supply fan at least once a month so it's spotless clean inside. What is causing this and what can I do.

 

[popatim]

have you tried reinstalling the OS ?

 

[Mountain Mike]

I did better than that: I installed Windows 7. I didn't do the upgrade, either, I did the full install