It's possible that the slot is damaged or a pin is bent. It's also possible that the card didn't make a good connection, or there's a piece of dust keeping one of the pins from connecting properly. Blow the slot out with air, inspect it for bad solders and/or bent pins, and if you find none, try a different card (or the audigy again) and see if it connects.
It's also possible (not knowing anything about the audigy's) that the new one requires bus master capability and that slot has its bus master turned off (or vice-versa) in BIOS. I'm reaching into territory I don't know about here, so I'm sorry if it sounds vague - but it is vague because I don't know.