I have a 1.2 ghz Atholon K7 (K7VMA). I purchased the machine with the processor installed. I have been having problems with overheating. I have the computer under a desk in a corner and it was performing horribly. The bios indicated it was operating at 62 C degrees/143 F degres.

I pulled it out from under the desk and opened one side of the case and the temperature immediately started to fall. My intake and exhaust fans (1 of each) are working fine.
Why did it overheat and what is a normal operating temperature? A technician at a computer store said that it should not be above 120 F degrees. My computer at work is a similar AMD operating at 129 F degrees with no problem. Testing my machine it remained at 131 degrees F with no processor function. What is a good temperature and would different glue (if there is any) or a different fan be the best upgrade?
I downloaded a burn in test, but is there any other way I can check for CPU and mainboard damage?
Please help!!