i have a system sitting right here with a P3 450 Celeron that displays the following strange and uncorrectable thing (until now) : if i leave the mobo under power, there is no problem, it runs fine.
When i cut it from the power with a hard switch, it will not start after i reapply the power. only after several tries, it will eventually power up. It will not have the cpu fan or the power supply fan running then. (when it does not pwr up)
I already replaced everything, memory, Pwr supply, disconnected everything, got it out the case, everything possible. So it is the mobo or the cpu.