Help HFSS stops working when ati catalyst is installed

Hi, I am stuck at a very strange problem. I have core i7 with external ATI GPU installed. When I try to install GPU driver, HFSS stops working. It doesn't even start after installing driver. The problem is that only two ati catalyst 12-3 and 12-4 support my GPU. I have 7870 GPU. Please help, I have tried both of the catalyst version