Help needed with OC old P4 1.8A

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I have this cpu for two years now. I have overclocked it to 2.4GHz ran cpu testes for 6h and it worked fine. Temp. went up to 53°C. I also ran 3DMark over night and it worked fine. System is overclocked form very begining and works fine BUT some games (not all) crashes!!!? I don't know if it si cpu because otherwise it is working fine and it usually crashes at the begining of the game so cooling shouldn't be a problem.

Strange thing is that it sometimes crashes competely (i have to restart) and sometimes i get error from ati driver:

*"VPU Recover has reset your graphic accelerator as it was no longer responding to graphic driver commands."*

funny thing is that after that crash game runs well and doesn't crashes anymore!?

I have radeon 9500pro card and this happens even when the card is not overclocked.

Well system doesent crash when cpu is not overclocked. I have Epox 4sda5+ (SiS 648) motherboard. I dont know if it has agp/pci lock but i think that when i overclock FSB form 100MHz to 133MHz agp/pci clock runs at default speeds??

but i think it is not cpu since i sucesfully ran many tests and that crashes ocours only at specific games (other run fine)

so what else could be problem?? HELP