Thanks a lot for suggestion. I thought to buy a better PSU but I was
waiting a confirmation from somebody who already had the same problem
and solved it this way.

I'm gonna post the results.

"N.S.Ng" wrote in message ...
Hi,

I did have similar symptoms with my P4PE w/P4, 2.66 especially running 3D
games programs. I changed to a better power supply, Antec 430 watts psu.
Problems gone. If your psu is one of those generic ones that came with the
casing, it might not have adequate current, resulting in voltage drop.

Regards,
N.S.