I found this from an earlier thread on AGP cards,so it may be worth checking what the voltage supplied by the mobo is and what the AGP card takes
I just read that 8x AGP Pro sockets work at 1.5v rather than the more usual 3.3v. Apparently some boards refure to boot unless a 1.5v card is installed.
AGP details:
8x = AGP 3.0 supports 1.5v cards.
4x = AGP 2.0 supports 1.5v/3.3v cards.
2x = AGP 1.0 supports 3.3v cards.
Some 8x boards now support 3.3v 4x AGP. As far as I'm aware, you cannot use 2x AGP - THIS WILL DAMAGE THE PORT.
Some mobo's with 8x AGP ports have a jumper to change the voltage, so its always worth checking your manual carefully.