"... without deleting the first driver first..." CANNOT DO THAT !!
Please follow these steps all over:
1. Control Panel -> Programs and components -> ATI install manager
2. Proceed and choose the last uninstall option -> uninstall all ATI components including ATI install manager
3. When successfully done, reboot
4. After the uninstall and reboot, to make sure just in case, download Driver Sweeper and apply it for ATI ONLY! 5. Reboot
6. Finally, install the Catalyst you have downloaded from the support site, and when successfully done, reboot.
7. Hopefully enjoy : )
Never ever install new driver versions without prior uninstalling tne old ones !!