While you did post in the Windows ME forum, it appears your question is not about Windows ME.
However, if you have an apparent good Socket 423 CPU, then I found replacement boards from compgeeks.com, newegg.com and other places. I also put such in a new case&powersupply since it's rare to find the new board to fit in the old HP case.
This is just above a beginner's level since we may have to reinstall the OS and the motherboard drivers too.
Motherboard gone... can't find one from HP.. are there any aftermarket boards that would work?
This is the early Pin 4 (large) chip..