encyclo - 12:39 pm on Mar 16, 2004 (gmt 0) If it's not that, which version of Windows are you using?
It could be a hardware problem. Is the processor overheating? You need to see whether the internal fan is turning properly, and not filled up with dust. Note, I'm not talking about the big external fan which makes all the noise.
If it's not that, which version of Windows are you using?