Months ago one of my main computers running winXP crashed. At first I
thought it was a software issue, and reinstalled XP. However, the
video seemed to struggle upon installation. So I put in a another hard
drive and installed Ubuntu Linux. It worked fine for a few days and
then the video on the monitor also begain to freeze and lock up the
system.

Now, I can't get the computer to POST and the mobo complains about the
AGP slot.

The problem is that no matter what video card I put in, the video card
fan will not spin. So that rules out the problem being the video card.
So my question is, how do I determine if the problem is the
motherboard or the power supply?

Everything else works fine, so that leads me to think the mobo may be
the problem. But how can I be sure of this?

My mobo is an Asus A7N8X Deluxe

This computer isn't old old, and I have already bought a new machine
for my main needs. But I would like to bring this machine back to life
as it would be good as another extra computer. I don't want to spend a
lot of time tinkering around trying to fix it if I could spend ~$100 to
replace the correct part(s).

Thanks for any advice,