If you think it's a temperature issue, take your side panel off your case and see how it goes
Scan for Viruses/Spyware and other generally nasty stuff.
Run a disk cleanup and defrag.
Have you got all your latest drivers installed (especially for your Chipset)?
AMD X2 4400+ Toledo 1MB/Asus A8N-SLI Deluxe/2GB Kingston HyperX/SLI Gigabyte 7800 GTX 256MB/Creative SB Audigy 2 ZS Plat w/ Creative Inspire 6.1 speakers /180GB Hitachi PATA/19\" AG Neovo F-419 LCD/OCZ PowerStream 600W PSU/WinXP Home SP2