HELP!!! cpu makes system lockups

[yenz]

ok need help i have an intel celeron 1 gig proceser with 256 ram i just got the proceser my old one is a 400 mhz my board supports 1.2 gig when i boot up into windows and run any program that takes 100 percent of the cpu usage example (dvd clone) (nortan anti) and so on after a couple of min of running the program with 100 percent usage the system will freeze totally and i hear my pc bog down when it freezes i cant do anything after this point it's a total system freeze now i no it has to do with my cpu becuse when i put my old one back in the 400 mhz and run the same programs the system wont freeze but when i switch the cpu back to the
1 gig and run something that takes 100 percent cpu the system will lock up other than that if i stay under 100 percent cpu usage the system is fine my mother board is a intel D815EEA2-D815EPEA2 and my bios on the board are up to date (p21)

the 1 gig intel chip reads 1000/128/100/1.75v
celeron sl5xt

any help would be great thanks

[Callero]