I had an AOpen motherboard here that I got for a buddy, and after a couple of months it started behaving poorly, in a very similar fashion to yours.

We eventually swapped out the PCIe video card for a PCI one, and it suddenly was healthy again. So we RMAd the video card, eventually got a replacment, and.. same problem. So this time around we RMAd the motherboard, and the identical replacement has been working fine for the past year and a half.

Cheers