Asus customer Support:
There are no specific settings required to install the card, the GPU should be picked automatically by the board.
In this case I recommend you make a CMOS reset of the BIOS by taking out the CMOS battery for 3-5 minutes while the PSU is unplugged. While the power cord from the PSU is still unplugged, press the power button down for 30 seconds to power discharge the unit. Then place the CMOS battery back in, plug in the PSU and try again.
Please re-install the card into the slot as well.
If it is not detected please return the board for RMA .