As you are having issues installing the driver and have had an Nvidia card installed prior to the AMD 7970 I would first run DDU Official Display Driver Uninstaller DDU Download
once you have downloaded this run DDU it will prompt you that it will reboot your system into safe mode once in safemode select the uninstall select Nvidia from the dropdown box and then select Clean and restart once this has completed you should be able to install your drivers as long as the AMD download is not corrupt.
Also when you downloaded the AMD drivers did you go through the options and select the correct driver rather than the auto detect ?? if not do this again and download the driver manually via the drop downs