well what if I'll tell you that I'm using Audigy 2 in same SLOT that your motherboard has?
check your slot closely, it might have something stucked in it,
have you tried it on all slots? and make sure you are putting it into WHITE slots. (as ur brown will already be covered by your AGP card)
* press in card, slightly and in 90 degree angle, DO NOT TILT
Intel Core2Quad 2.66Ghz 12MB L2-Cache
4096MB DDR Kingston Hyper-X
XFX 9600GT AlphaDog
Seagate 2 X 320GB SATA2
LG L246WH Flatron 24"