[Hampshire] Motherboard problems?

The box in question has had a variety of problems in the recent past: two USB
PCI cards erratic (sometimes connecting at USB2 and sometimes connecting
identical hardware at USB1.1 speed); two optical drives (one brand new) which
I cannot access to boot.

I have: installed a new USB2 card; installed a new optical drive; changed the
BIOS boot order to various permutations - the BIOS always tried to boot from
something else other than CD, even when only CD was set (it simply did not
offer to boot at all); and changed the CMOS battery, restoring the
motherboard in the process and changing only the boot order. The booting
problem remained.

I have googled extensively, and found no suggestions other than those I have
tried, tho' I realise that it might have been worth swapping the IDE cables
round in the IDE channels to see if it made a difference.

Any suggestions as to what to do gratefully received!

Lisi