Hi Feng,
if you do have W2K, you might want to try booting using the W2K-cd, using the recovery console and then disabling all the BackupExec services.
Disabling the SCSI device service that has the tape-unit attached to it, might help too, if you are sure it's the only device attached to that.
Of course, make sure you document exactly what you disable, what the original state was and are certain you can go back.
Try this and say what happens
Ivan