first of all, it would be helpful if you give us any information about your mainboard.
I recommend to look it up in "Total Hardware 99" (http://www.uncreativelabs.de/th99/
and report the exact or most equivalent model.
About your RAM problem.
After you may found your mainboard, you may see a "memory arrangement" table which shows
the possible arrangement of RAM sticks (and so memory) you can combine with your mainboard.
Nearly all pre-1995 mainboards have a typical but strict order,
how memory sticks have to be in the sockets.
e.g.: 2x 8MB Sticks on Bank1 (one or two slots make up a bank, type depending)
and Bank2 will give you 16MB RAM.
2 Sticks on Bank 3 & 4 may won't work at all.
One on B1 and one on B3 may give you only 8MB or none.
About your CPU ID problem.
I have no clue what it could be. I don't have a decend 486 machine. Only low-end SX.
Hope this helps somewhat to clear up your issue.
When there's no more room in RAM programs will reflash the ROM.