Hi,
Please understand I am not proposing a solution based on any particular computer knowledge.
It would seem to me that your problem is one of the computer not seeing a charge or battery , one and the same when you think about it.
Now you suggest that you changed the CMOS battery and that the battery works O.K in another computer.
Logic now makes me think the battery is not making a connection when you place it in the holder on the mother board.
Given my experience with replacing CMOS batteries, somewhat dated and by no means VERY often.
None the less, i suspect you could find two spots not far from the battery connections, where you could use a very simple volt meter to test, to see if you have indeed succeeded in making a connection with the battery and your mother board.
If you are unsure about the use of a meter, ask everbody you can find if they have a volt meter. the fiorst person who says "yes" will proberbly know how to test for a voltage. offer them a known good battery, something like an AA or AAA cell will do. Ask the meters owner to test it for you. If they can easily do that by showing you the voltage. let them loose on your mother board. Asking them to check the battery is supply the voltage you need.
I hope this is of help to you
good luck