Seagate DAT Drive..failure

We have a 12/24gb DAT internal in server. We have had several, actually many, failed backups in last couple of months. We are using Backup Exec 7.3 ..and our firmware for tape drive is 735B. We were told to clean drive, did that.. and upgrade firmware. I have downloaded a firmware upgrade, but excuse my ignorance, am unaware on how to get a true DOS prompt in NT server 4.0. It cannot be done from Windows. Any help would be greatly appreciated. Thanks!