When you see 'No Tape Drives' in the GUI this is the graphical representation of running the command
cd \Program Files\Omniback\bin
devbra -dev
If you see no drives here, then my next step is to look at the Windows Device Manager
On the Media Agent, go to Windows Device Manager, and look for Tape Drives. If you find this, see if it has a |+| sign next to it, enabling you to Expand
The Device Manager, is going to show two things that Data Protector cares about
Media Changer
Tape Drives
If one, or both, of these categories are not seen in the Device Manager, it is not a Data Protector issue. I would check the cabeling to make sure that everything is connected, and terminated properly. You may also want to reboot the Media Agent to rediscover SCSI-attached devices, and reboot the Tape Library itself