Here is what's happened so far. The whole story but short. MSI MS 6545 850 Pro5 Mother Board. Pentium 4 1.5 Williamette Samsung RAMBUS PC800 256mb, now 768mb. WD 7,200 40gig hard drive. Radeon 9600XT The story: Overclock the CPU, no matter how high or low & the system will reboot, no warning. Then won't post till defaulted. (that's not the problem) Get myself a P4 2.5 & as soon as I run the second torture test in Prime95 it reboots back into windows till it has a sissy fit & does it again & again & again even when there is no load. Did a memory test. All OK. Swapped the 9600 with the old geforce. Still rebooted. Put the 9600 back in. At the same time took all the pci cards out. Still reboots. Put cards back. Upgraded PSU to Antec TrueBlue 480w. Still reboots. Returned the 2.5 & got a 2.6. Damn thing still reboots. As I have done just about everything there are only two things I can think of. 1/ Something in the BIOS is set wrong. I've tried default & optimised default. 2/ The board itself is cactus. When it first came out it only supported up to 2.0ghz. They now say it will take a 2.6. It has the latest BIOS. When I run the 1.5 the system is as stable as the day I got it. What do you think?