Check out the following link.
http://www.hardwareanalysis.com/content/topic/33605/
As the CMOS battery starts to die things like CD-ROMs, Floppy Drives and finally the hard drive will fail. In Windows and Linux your CD-ROM will not show up in the OS as the CMOS battery starts to die because the BIOS cannot detect it. We are not talking about boot sequences. It will not even show up in the OS let alone the boot sequence. The clock will start to fail first but eventually all boot devices will be affected. Trust me a totally dead CMOS battery can stop your computer form booting. Especially the older BIOS systems form 1997.
I should ask if you have ever worked on an old Pentium II style motherboard? They used to have dip switches and jumpers back in those days.
I am not saying fore sure this guys computer will work after changing out the CMOS batter because his BIOS could really be corrupt and with how old it is they wouldn't be able to send him a new BIOS chip.