Is My Computer Overheating?

[chakka35]

I run Windows XP. Recently my PC has started behaving erratically after somewhere between 30 minutes and a hour's use. When I switch off for a while and then reboot it runs OK and then the cycle repeats. I suspect overheating, a suspicion made stronger by the fact that the working periods are much shorter in this hot weather.
I have checked that all fans are working and have cleared out all dust including from the heat exchanger on the CPU.
Is there an app that will tell me whether my PC is overheating and why? If not, how can I tell which fan isn't working properly? Any help much appreciated.

[bassmanjack]

MSI Afterburner is free. It lets you see all temperatures (CPU &GPU) and control fan speeds manually or automatically. Great for gamers.
Get it here...

http://event.msi.com/vga/afterburner/download.htm

Tutorial on youtube link.

http://www.youtube.com/watch?v=vWxCcscrrjM

[chakka35]

Thank you, bassmanjack.