Slow Computer

My laptop has recently been mishandled. It was left outside in the cold for about 8-10 hours. Since then it has been running very slow. Specifically the CPU usage jumps up and down from about 60 percent to 100 percent even when the computer is not doing anything.

I have tried to eliminate a virus as the source of the problem by running scans with symantec, avg antivirus, bitdefender online, as well as analyzing hijackthis logs, and doing spyware scans with adaware and spybot.

I have run hard drive maintenance such as chkdsk, and defrag. My laptop is currently dissassembled, because I was looking for physical damage to the hard drive, motherboard or the processor.

Before I reassemble the computer, is there anything I should look for in terms of physical damage?

When I reassemble my computer what should I do to fix this problem?

Please help.