PC freezes at random

Problem: My Pentium IV 2.4GHz, 1 Gb RAM, Motherboard Intel 865PERL tends to freeze completely without any warning. Mouse and keyboard do not move/work only solution is to reset.

I could not identify any pattern. Sometimes happens when I’m reading e-mail or browsing the web, sometimes even when the PC is idle.

I believe it is a hardware problem because the same problem happens when I’m running Windows XPSP2 and also Linux (Fedora). PC temperature is within OK ranges, for different reasons I already replaced video card, HD and power supply but the problem continues.

Microsoft Memory Diagnostics and Intel Desktop Control Center do not show any error.

Any Ideas?