My wife and i returned home after a 40 day absence.As a precaution to electrical surge events we deprived all our computers of a power connection. On PLUGGING them back in all but my wife's HP desktop running Win ME (gives you an idea of it's vintage) ran normally.Absolutely nothing happened on it.The same as if it was still powerless. My logic suggested to me that a deterioration of the CMOS battery to dead was the only thing that made sense given that the computer worked fine until our departure and to my mind nothing could have affected it's performance in our absence. So with a google search parameter of "will a computer still work if the cmos battery is dead?" i sought enlightenment.After reading a great multitude of the answers they ALL agreed the computer should still work (with limitations) without a functioning CMOS battery. I cannibalized a CMOS battery from another computer. Lo and behold HP working again as it should. I advance this topic in the event that others may find it useful when facing the same issue and to encourage them to try that solution.  truenorthThank you, bluetooth.
That goes to show that just because a large majority of EXPERTS think something can not happen, it still  could happen.
Makes one think of the question about the firmware on a automobile that was reported to have run AWAY alteration problem. After a STUDY of about a small number of cars that were normal, they determined that thee was no problem at all. It never happened. Had to be a mechanical failure.

Using that logic,
your experience -
with the CMOS battery -
never happened.     
Newer PC's will boot with a weak /failing CMOS battery...
However this did not hold true on older models... Quote

The purpose of the CMOS battery most often today is simply to allow your computer to REMEMBER what time it is. I think of it as a glorified watch battery. If the battery dies or is removed, then when your computer boots it will have forgotten the current date and time.

Typically the CMOS battery no longer affects whether or not BIOS settings are remembered. Most of those settings are kept in a type of dedicated flash memory, not unlike the kind that might be inside a USB flash drive. In the past, back when the battery was actually powering "CMOS RAM" to retain those settings removing the CMOS battery would cause your BIOS to lose not only the date and time, but also any customizations you might have made to the BIOS configuration.

http://ask-leo.com/how_often_should_i_replace_my_cmos_battery_and_what_does_it_do_anyway.html

my CMOS settings reset when I remove the battery.

I guess it's a battery powered flash. 

It is that dated motherboard you have!