Hi Jacob,
Please check in the device manager if you can see media changer....
If yes then do not install drivers for the same. Make sure that it is showing you as a unknown media changer
If not then shut down the server, switch off auto loader, remove the SCSi cable.
Then reconnect the cable, switch on autoloader & switch on server
Re-check for the media changer
Check that you have latest SP & hotfixes are installed
Install tape device drivers which is provided by Symantec and check for the device version.