I bought an old Diamond Multimedia MX300 sound card.  Oddly, it
arrived with no backplate.  I decided that I could test it without
one.  I did so, and switched on my PC, and I didn't have any luck with
it.  On some occassions the BIOS reported no new card had been
inserted, and on other occassions the BIOS reported "Unknown Device".

I cleaned the "PCI contacts" on the card, and then did something
daft.  Because it had no backplate, and because I wasn't paying close
attention, I put the card back in to the PCI slot *the other way
around*.  Please believe me, it wasn't *that* stupid because a) with
no backplate present, there's nothing which physically prevents this
from happening and b) the MX300 card has a kind of gold coloured
"connector-thing" at the other end, which if you're a bit of a blind
bat like me, you *could* mistake that for the "audio port bits" at the
other end.

I turned on the PC, and for about 1 gazzilionth of a second the CPU
fan went round, then stopped.  No life.  I decided that I'd done
something pretty bad, so I pulled everything off the mobo, got another
one out (good job I've got piles of these old things), and powered it
on.  No life.  I swapped the CPU over for another one and bingo, life
again!

I don't know for sure whether I also broke the original mobo, and
possibly extinguished whatever life was left in the sound card.  I did
try it inside the "new" mobo, but I couldn't get the BIOS to even see
it, so perhaps I finished it off?

Didn't get much done today!

(Board: Supermicro Slot 1 Pentium III)