Above machine powers on, fans run etc. Most times, no start-up beep, no video. When I power it off and on a few times. then POST proceeds, and machine boots to Win XP which then fires up and runs fine. Sometimes machine shuts down in the middle of POST. Accessed BIOS and reset to fail-safe values, F10 to save and machine just shuts off. instead of reboot. No POST again for awhile. I have swapped out the memory with other known good memory, tried a known good PSU, successfully updated BIOS from level F6 to F8, disconnected all drives, PCI cards etc Same problem. Also, machine just shuts down after selecting RESTART in XP, or clicking restart now after a software/driver install. The reset button usually will cause a slightly delayed shut down and I only get a successful POST after numerous resets or power offs. Machine has on-board video and if I install an AGP card instead same issues. I thinking just a bad MOBO or
some kind of power management glitch. Suggestions would be appreciated.