Welcome to the forum
Make sure as said above that you have uninstalled the old drivers completely and that you installed the latest drivers from the ati site, if not they can be downloaded HERE
also go to your ati display properties (Control Pannel > Display > Settings > Advanced) then go to Overdrive and check the cards temperature.
Gigabyte Z87M-D3H l Pentium DC 3.2GHz l 16GB Ram l 64GB OCZ SSD l Radeon 7750 OC Edition l Windows 7 Ultimate X64
Dell OptiPlex 745 l Intel C2D E6600 2.4GHz l 4GB Ram l 64GB OCZ SSD l Windows 7 Ultimate X64
Lenovo ThinkPad T61 l C2D T7700 2.4GHz l 8GB Ram l 60GB Kingston SSD l Windows 7 Ultimate X64