If it's seen in the Windows Device Manager, it means no comms issues between your SCSI card, Windows and the tape drive. So the problem is with Backup Exec and the tape drive.
In this case (and I do it when replacing any drive, even a drive in an autoloader), I'd run the Device Configuration Wizard from Backup Exec. Select the option to install the Symantec drivers (if you check in Device Manager, and double-click on the tape drive and go into Drivers...does it show Symantec as the driver?), and delete any devices that no longer exist. Sometimes BE needs that to happen, even it it shows up in the application.
Lastly, make sure that you have disabled Removable Storage...not needed with BE.