Endless Blue-Bar Startup, Randomly

I'm having an issue with this system:

• Mobo - XFX nForce 610i
• CPU - Intel Pentium D Desktop E2200
• RAM - PNY 1gb (one DIMM) DDR2 667
• HDD - 80gb Seagate SATA
• OS - Windows XP Pro

This system is a point-of-sale machine, whose sole purpose is to run Peachtree Complete Accounting to access our company database. It is a member of our domain on a Windows Server 2003 machine.

Here's what's happened so far:

I purchased the parts two weeks ago, assembled the system, installed XP (original CD), installed drivers from motherboard CD, installed Spybot S&D, updated fully, installed latest nForce 610i driver, joined the domain, and installed Peachtree. I shut down the system and rebooted several times, everything worked fine. After a few days, without ANY changes in hardware or software, the system exhibited the endless blue-bar and would BSOD with instant reboot if we left it long enough. Safe mode caused the system to hang for a few minutes with the last line on the screen indicating the loading of "mup.sys," and it eventually BSOD with instant reboot.

Thinking that the problem was the drivers, I did a full reinstall and kept the included drivers, and only updated XP to SP2. This gave the same results. The reinstall was on Monday, it worked yesterday, and this morning it had the endless blue-bar. I managed to get it to boot up by selecting "debugging mode" from the safe mode selection screen, and I uninstalled the drivers to replace them with the latest ones. After that, I shut down, started up, logged onto the network user, restarted a few times, and made sure everything was fine. After a few hours, a taskbar notification message comes up stating that "SysEvent.Evt" could not be saved, in the form of a Delayed Write Failure message. The taskbar and Start were frozen, and ctrl-alt-del wouldn't bring up the task manager, just hide everything but the desktop background. After that, it hasn't started up normally or in any kind of safe mode.

The only possible solution I've found is some anecdotal evidence of the hard drive brand being incompatible. The only other drive that I have on hand is another Seagate, which is a 160gb IDE drive. Are there any other options or solutions?

I considered the RAM, but it works fine after reinstalling. I'll definitely run a memory test if anything else happens.

When I left work, it was working fine with the 80gb IDE Western Digital that I gave up. I'm guessing that if it makes it through tomorrow and Monday, the HDD was incompatible.