Sporatic re-boot

Power supplies will act in this fashion.
It is much cheaper to replace then the MB if you are not sure.

Does it reboot when you try to use the modem and the mouse at the same time?
When you use the modem and the sound-card at the same time?

Has the computer ever worked?
If so, did you recently add some hardware, or update some driver, or "flash" the BIOS?

Yes the computer has been working fine right along for a few years.  No new hardware and the only software was the MS Y2K upgrade to Windows95, Office97 etc.  No flashing of the BIOS was done.

when does the system reboot?  Yes, this could be power supply related but many times is caused by something else.  Knowing when this happens could help us.  what are you usually doing when this happens?  online? games? printing?

Actually the user whad an excel spread sheet open but was turned around doing something on her desk at the time.

how many times has this happened|?

About 3 times today.

various programs running?  never at a consistent time?

if so, motherbaord or powersupply is most likely but you can try things like removing the "extra" components like sound card, modem, network card and see what happens.  I realize this might take away some functionality but could diagnose whether it's another component causing this.  Most liekly though, it is the powersupply or motherboard.

also, try things like changing power outlets, removing surge protectors, changing cables, etc.

How's the electrical power into her office?
If it fluctuates, and there is no surge-suppressor between the wall-outlet and the computer, any fluctuations in the power can "upset" the computer.

Occasionally, an overhating CPU will do this.  More often, it just freezes, but if any of the above suggestions don't work, try another CPU.

Bill

it can be a IRQ/PCI conflict too, try moving the cards to different slots

//Jonas

> try moving the cards to different slots

This is very unlikely to solve the problem.

though it shouldn't have been posted as an answer considering that it had to be said with a word like "try", I have seen the proposed advice resolve these types of issues.  I work at NEC and we had a problem exactly like this with one of our Athlon based systems.  The system would reboot while online and while playing 3D games.  We found that A) changing modem to software flow control and B) moving the modem from the first PCI slot on the FIC SD11 motherboard resolved the issues for most customers.  This was due to the fact that there were issues with the AGP and first PCI slot competing for resources and though it sounds strange, was causing the reboot problem.  We also found that removing the modem and sound card from device manager, letting Windows reinstall the modem first, and manually installing the sound card again, also helped.  On a side not, FIC ended up manufacturing a new revision of the board due to the fact that in cases where the issues were not resolved, we were swapping the mobo and processor for a PIII based configuration and sending them the boards back.

alayne, have you noticed whether this happens after a good amount of time using the computer or could it happen a few minutes after boot?

I tried swapping out the surge protector and then swapped out the  video card,  I swapped these 2 FRU's out after receiving 1cell's comments.  

1cell if you'd like to pose your comment as an answer I'll give you the points.

Sorry, I didn't include in the previous text that yes it did solve the problem.
The line about re-moving adapter cards helped me try to swap out the video card.  Never knew a faulty video card could do such a thing but once I changed it, the sporatic re-booting stopped.

Thanks for the direction !!

glad I could help.

demo007, I'll post a question for you in this category to share the rewards.