Did you install the right drivers?
In the BIOS is the GPU Auto selected?
How much memory you had allocated to the GPU in the BIOS?
I had a little problem, different from yours with a PC that I fixed, that were basically almost the same, but with graphic corruption and a very slow system.
The solution was that in the BIOS the GPU from Intel had only 8MB of video memory allocated. I allocated 64MB for video memory to the integrated GPU and the slowness and graphic corruption had disappear (strange I know but it were the reason).