Backups Never Run

Need some help. I have been running Backup Exec 8.6 on this NT 4 server for about 2 1/2 years now. All of a sudden last week, it decides that it's not going to backup anymore. I have tried installing the latest release of 8.6 and have uninstalled and reinstalled the tape drive. When I tell a job to run, it just shows up under the Activity monitor as Scheduled, never runs and eventually shows Missed in the status column. The software shows the tape drive as online. Can someone please help?