Help - I cannot use any benchmark programs. When it gets to graphics, it fails. R9 280x

Well, a couple of things regarding this

• I cannot boot unless I boot with onboard graphics. If I boot with the GPU, it gets hung at the apple boot screen.

• When I go to about mac, it shows AMD R9 280X.

• When I use Novabench, it shows "null"

• Geek bench sows the GPU, but fails when it gets to the graphics portion of the test.