Your problem is that you must first insert the tape. Then select the tape drive and right click on it. A menu will appear, select to inventory the tape. This will run as a job. Check and see if the tape shows up in the restore availability section. If not you will need to catalog the tape next. If after you catalog the tape you are unable to select it for restore, I think your having some serious problems with your data. I would check the logs to be sure that your backups are successful