I've been running my AMD (ASROCK K7VM2 Pheonix Award BIOS XP PRo SP2) fine since 2003. I just upgraded it adding a second stick of 512MB (1GB total) and a CD Writer.
Shortly afterwards I was geting occasional system hangs and every time I rebooted "CMOS Checksum error". I replaced the 3V battery with a new one.
Now I have the following situation which I can repeat at will:
1/ I remove the battery and leave be for 1Hr or so...
2/ I replace Battery
3/ Machine boots with POST and
"CMOS Checksum error - defaults loaded" and
"Warning! CPU has been changed" (it has not)
4/ If I hit "F1 Continue" the machine boots into Windows XP no probem...
5/ On subsequent reboots I no longer see the "Checksum" error but I still see the "Warning! CPU has changed message". So long as I hit "F1 Continue" on boot up the machine boots into Windows XP Pro no problem...
The problem only comes if I hit DEL to go into the BIOS utility. If I do this it screws the machine. The BIOS menus come up fine but even if I "Exit without making changes" the machine is screwed. Basically from that moment onwards the machine will not boot properly.
On power-on I'll see a brief Nvidea graphics card message... (Which always normally preceeds POST) then the machine resets and loops like this for ever (No POST or anything else!) Nvidea..., reset, Nvidea..., reset, Nvidiea..., reset etc etc...
The only way to fix this is to start procedure form 1 above....