|Some new ATI cards seem to have problems with older PCIe 1.0A motherboards. They work fine with PCIe 1.1 and 2.0 motherboards.|
For example, I have a Radeon HD 5750 that works great in my HTPC but doesn't work at all with my NF4 SLI (PCIe 1.0A) board. My brand new Nvidia GTX 460 card works just fine on the NF4 board.
The only thing I can suggest is to update your BIOS to the latest version. If that doesn't work, try an nVidia card.
Socket 939 | Dual-core Opteron 185 @ 3.2GHz | 4GB | 1.0TB | Win7 x64
GeForce GTX 460 1GB | X-Fi Ti Pro | A8N32-SLI Deluxe | Antec P182