This board has been my latest personal hell. Back in the year 2005, my Asus P4C800 Deluxe fried. After taking their time, Asus sent me a replacement board. I simply assumed that it was a Deluxe and reinstalled it. Unfortunately, it was actually a P4C800 Rev 2. There are three models of the P4C800: P4C800, P4C800 deluxe, and P4C800-e deluxe. From what I can tell online, the Rev 2 is actually the e deluxe, but it looks like a hacked together mix between the P4C800 and the e deluxe.
This is where I made a mistake. One night when trying to get suspend to work in Linux, I decided to flash this board. I flashed it without checking what bios version was already on there. Stupid. Worse, since I knew it wasn't the deluxe (because the updater rejected the bios), I assumed it was the e deluxe. As would be expected, after the flash, the system wont boot. Flash forward a few days, and I've managed to force a flash downgrading the system to a P4C800.
Now looking back, I honestly can't remember what the board was originally and which bios I first forced onto the board. Never flash bios when tired and in a rush. I still can't believe I did that. Anyways, the system suffered from random shutoffs. I assumed this was due to the flash. (Honestly I can't be sure one way or the other now.) Over time these flickers grew increasingly annoying. So, I tried another flash. That time I managed to brick the board.
Yesterday I received two replacement bios chips. (One is a backup for hot swapping.) The latest version of the P4C800-e deluxe bios works, but it wont reboot. The latest version of the P4C800 bios works and will reboot. Both suffer from the intermittent shutoffs, and both have bios errors referring to the IRQ routing table. At this stage, I'm pretty sure the problem either isn't a bios issue or at least isn't a bios issue that I can resolve.
I installed this board into a new case with new hardware and the shutoff problems ensued. This has brought me to the conclusion that the problem has to be with the board. Removing all hardware except the bare bones still results in the shutoff. Another irritation is the problem wont normally occur when the system is idle. Also odd is the problems happen most in XP, less in Ubuntu, and the least in Windows 7. I don't know what that means exactly, but it suggests that whatever is triggering the problem may be a deprecated technique that modern OS's don't use. Though it may be that the board is just getting old and needs to be tossed.
However, the two things that keep bring me back to suspecting the bios are: the coinciding timing of the first shut offs / bios flash and the fact that the board looks like a P4C800 with a Rev 2 sticker slapped on it instead of a P4C800-e deluxe board. There might be some bios out there that will stabilize this system that I have yet to find. I should probably contact Asus.
Although I'm sure this isn't the conclusion to this story, it should be noted that suspend still doesn't work. :(
Edit - 28/10/2010: This is the conclusion, because the pieces are now sitting in a box. My brother upgraded and let me keep his old hardware, which is newer than the P4C800. I'm now looking for a good way to get rid of this old hardware.