There are a number of different motherboard failures that will cause this. The vendor or supplier of the machine will be getting calls about it (they sold more than yours) and will collect a history on this issue and know what to replace.
The fact that it may boot and work proper is not very interesting. Nor is XP playing a factor yet since no OS is loaded yet.
After I have copied off the files that I can't lose (AKA backup), there are two items I would try prior to replacing the motherboard .
1. Reset the CMOS settings to defaults. WARNING! My machines use these defaults with no changes except for one machine which I tagged a note on what to change from the defaults. You know your machines well and will know what's not on the defaults.
2. Inspect the motherboard for the bulging, leaking motherboard capacitor issue. It's an epidemic problem (I'll supply a Google link to the articles) and will cause an error like yours. Complete with it may work after a few resets.
The Google -> http://www.google.com/search?&q=bad+motherboard+capacitors
I have a computer running Win XP pro. Recently, the following error message appeared and I was unable to boot up:
*** Hardware Malfunction
Call your hardware vendor for support
NMI: Parity Check / Memory Parity Error
*** The system has halted ***
I had not installed any new hardware or software.
I found this article which seems to address the problem at MS knowlege base:
What's different about my situation, however, is that it boots up and works perfectly fine in Safe Mode (with networking.) Also, if I try too boot it up in normal mode it will sometimes boot up and funtion normally for a short time before freezing and displaying the above error message (usually it freezes before actually booting, though.)
If anyone has any ideas or suggestions they would be greatly appreciated. Thank you.