Setup: I have a base P5B with second-to-latest bios (latest is a beta), 3GB generic korean memory, generic Gearex power supply, Samsung 250GB, LG IDE cdrom, 9600GT video and Intel E6420 @ stock. Computer has been stable for 2 years. I am now having these problems.
Problems: Random power-outs, 4-second delay then reboot, it stays stable about 5 - 25 mins.
And now it doesn't even have any video after the initial post screen.
What I didn't try: swapping cpus or mobos
What I tried: when stable, runs Performance Test with no problems
windows memtest passed multiple times
Tested power supply with multimiter and asus Probe II, seems fine, no overheating, or under-voltage
Temps are ok in the 30ies
Removed SATA drive, now trying to diagnose with IDE drives
Other important info: This board has the on-board JMicron IDE controller. At startup there's a 20sec delay as it detects the drives on it. From what I understand, the drives cannot be booted from because the drivers for the JMicron controller have to be present, so the drives can only be accessed from windows after the drivers are installed. No problem booting from sata drives or cdroms.
So, if I set the floppy to be the first to boot then there's about a 30 sec overall delay until the floppy is read. However now that the video is dead, it goes to floppy boot in about 5 secs. It's as if the JMicron chip is bypassed entirely! The computer does run commands, i.e. dir > file.txt, file.txt can be read on other computers.
It seems that the mobo is gonzo, any help or ideas would be appreciated!
sounds like a mobo problem...
normally when there is a delay when rebooting like you described, the motherboard is resetting all the bios settings to fail-safe settings, to try to fix a problem.
if you can, try a diff mobo