SL300 slows down every now and then

[malachont]

I, I have an XP SP3 SL300 Thinkpad, in random times (seemingly not related to what is run on the OS) the machine slows down to a very slow processing speed, I've tried to set all the cpu speeds to max in power settings but this still happens, its especially bothersome when watching videos as sometimes they start playing at half speed.

I downloaded all MS and Lenovo updates that seem related to this (bios, power...)
Any help appreciated...

thanks