Hello all,
I'm trying to track the source of a number of problems that have started occuring:

Computer won't shut down, restarts instead.
Sometimes restarting approx 5min. after booting.
A: drive will only allow 2 or three files to be saved from ANY program and then locks up.
Gives virtual memory error when you load Internet Explorer (Made the switch to Firefox I should have done long ago)

Replaced A: drive, same problem.

Here's where I really get thrown and makes me assume I need a new motherboard...

I decided to try and replace the HDD, just in case that fixed it (I have several new ones here anyway).
Thought I'd clone the old one and rule out bad HDD. Hooked up new (3rd) HDD in place of CD-ROM (2nd HDD already on same IDE as primary). Started up, and computer spun up but did not POST or even kick the monitor out of power saving mode. Went through every configuration possible and discovered that the computer will only boot in the exact configuration it is in now. It wouldn't even boot if I plugged an extra power cable into the HDD (I tried a couple).

I've got a feeling that I'll be replacing my motherboard tomorrow, but wanted to double check everything.

Any ideas?

P4IBMS motherboard
P4 1.5Ghz
512 RAM
Win2k

Just by what you just said, its more likly your powersupply, which is the reason why your ram acting up. (Bootup your system without the new drive take a Meter and check the 12vdc and 5vdc if it lower then 12 or 5 replaced the power supply, and yes the computer would run even thought the powersupply is bad, it just restart you wil get errors messages and plugging in any thing else will cause the computer proably not to boot up at all.

Sorry, I didn't mention that I'd already eliminated the power supply as the source of the problem. Checks out fine. Any other thoughts?

It have to be your ram or motherboard. Ram does cause bios not to accepted any change, and system not to bootup and restart every 5mins, but then a bad motherboard would also cause the ram not to work right and actup if you have another stick of ram try on this system see what happen.

before u kill the mobo trying isolating different peripherals....ie: keyboard, mouse, cd drives and any other peripherals that u may have attached.