I’m running Symantec BackupExec 12.0 on a Windows 2003 server. After I powered down my SCSI tape drive (Dell PowerVault 124t autoloader) it no longer shows up in Backup Exec in the device pool. 
 So far, I have 

* updated firmware on the tape unit
* reloaded drivers
* walked through the wizards in BUE
* updated patches on BUE
* restarted the server and the tape drive
* updated all drivers to the latest versions
* prayed
* run every utilities known top man.

Device manager shows the Tape unit is working properly and so is the SCSI Raid controller. I have walked through all of the tech notes from Symantec and other support blogs. I remember about a year ago I had this same problem and Symantec did a webex and repaired it. I think (cough cough) that they deleted some files and touched up the registry. I really can't remember. What else can I try to resolve this issue? Thank you in advance for your help.