PC crashes when playing flash and Mp3s

Ive got a P3 550hz, 300 sd ram,10 gig hard drive,QDI mother board,ATI all in wonder card, creavtive LIVE sound card.

It was working fine, till I started to notice that the PC would lock up when playing flash movies, it also froze up when playing music files MP3s.

Ive tryed reformating it and sticking a new XP , new drivers and Direct X9 on it but still it happens.

Ive even replace the video and hard drive to see if that will help .. but no joy, even stuck more memory but it still locks up

Any ideas would be apprciated, I think the processor might be knackered .. but I never see it using more than 98% of its resources