As previously metioned here, I had boot issues with my new Motherboard, and my external Western Digital USB hard disk. But it’s really a motherboard fault, or not? It turns out other cheap USB enclosures dont’ endanger my boot like the WD hard disk does.
A little google-fu revealed that it’s indeed Western Digital fault, and not AsRock.
See the original post here. The solution, as it turns out, is to simply modifying the USB legacy option disabling it. The article mentions a Sony Vaio but it worked also for me on an Asrock motherboard. It seems to me that Western digital has something to fix, instead of bouncing the problems to other brands…
No more failed boots, it worked flawlessly since.