processor damaged?

Hi, I have a question for you that's a bit important,
I have a Fujitsu Siemens Amilo A1630 notebook with a AMD Athlon 64 3700+
installed (running Vista x64 and Ubuntu 7.04). Two days ago, I was
playing with a game and suddently the PC shut down. I turned it on again
and I had the same problem, and since that day this problem occurs every
time the processor is used in a heavy way (only using it @ 800Mhz seems
to keep the machine alive).
I used RMClock in order to run the processor at its real speed (2400mhz)
because Windows Vista does not provide Cool 'n' Quiet Drivers to do it.
The same problem occures now also in Ubuntu, that in the loading phase
shuts down when a fast processor speed is required.
I started thinking that the problem could be connected with a damage
occured to the CPU the first time it shut down while playing that game -
maybe for a overheating reason.
Someone could help me?
Thanks a lot!!!