Memory Size Decrease

I found this old dell 4100 at my school. I was told "it dosent work" so i took it to try to fix it. When I turned it on for the 1st time i got the error "Memoery Size Decrease" I restarted a few times and it told my to replace the CMOS battry. So I replaced it and still got the error. The post i hear: 1 big beep and 3 small ones. But it changes, sometimes I hear more than 3 beeps. Sometimes it beeps and dosnet even mention the "Memoery Size Decrease." If ya need anymore info please ask, i really wanna get this up and running.

Check this out! http//do/...

Looks like you need to replace the motherboard, are you a bad enough dude to do it? (Is it worth it? Or just keep it around for parts!?)