First, please understand that DP 6.0 is years out of support, and that may limit what help we can offer
On your Windows media agent, go to the Device Manager. Are you seeing a Media Changer, and/or Tape Drives? if not, then this is outisde teh scope of Data Protector, the Operating system is not even seeing the library. I would suggest that you check your cabling, and possible, reboot the Tape library followed by the Media Agent to try and rediscover the devices.
If can see tehe devices in the Device Manager, at theMS-DOS prompt on the Media Agent, run
cd \Program Files\Omniback\bin
devbra -dev
This should show all locally-attached devices. Depending on what thsi shows, you might eb able to manually configure the library