Hello and welcome to the forums
I always recommend installing the latest drivers but not this time,because many users found 10.7 unstable and buggy so try an older driver like Catalyst 10.5, do a clean install of it,here is how
1_Download and install "Driver sweeper" from Guru3d.com and install
2_Go to add/remove programs and uninstall the driver and reboot
3_Boot to safe mode and open driver sweeper,then click on ATI and then click on clean
4_Reboot and boot normally to windows and install the new drivers after that you need to restart,and its done
Also try disabling Windows Aero and see if it helps.