I am not sure why you are having trouble, but I do not have any experience with that particular motherboard.
Here are a couple of suggestions that might help. Make sure you are using the latest BIOS and the I/O options in the BIOS are set to default settings.
I thought of something else you might be able to try. If you are using the onboard video and have not added another PCIe adapter, you should have 2 PCIe slots where you can add Ethernet adapters. If you have not already tried installing the adapter in the other slot, you should try moving the adapter to see if the adapter is detected.
Thanks for the ideas.
I have tried both PCI slots, both behave the same.
BIOS is almost the latest version (v1.05, latest is v1.06) and the change log does not mention anything what could seem related to PCIe, it's only support for newer CPU's.