It sounds like heat might be a problem, so you should try to eliminate it as a possibility. You can try to control the processor speed, and possibly put a ceiling on your voltage, doing so might lower your heat so that you can determine if something else is wrong. There are two programs I've used to manually control processor speed/throttling:
http://www.diefer.de/speedswitchxp/and
http://www.pbus-167.com/chc.htmThe second has the advantage that it may be able to directly control the CPU's voltage, in addition to controlling the processor speed and it can also monitor the temperature inside the laptop if you have the necesary sensors. The only annoying thing is that in order to work it requires Microsofts .NET framework version 2.0.