Do a clean uninstall.
1_Remove the driver from add/remove programs.
2_Download "Driver Sweeper" from here:http://www.guru3d.com/category/driversweeper/
Then go to safe mode and open Driver Sweeper,choose ATI and click remove.
3_Restart and boot normally to windows and install the driver again,after the installation restart the PC and see if it works then or not