Can you start it manually from a DOS box ?
If not what error, what error does it give ?
What backup software is it ?
Does it have it's own scheduler ?
Is the system clock set correctly ?
Is it trying to start when it's meant to finish ?
If you are struggling with the AT command, try using WINAT. Whilst not the best GUI represenation of the AT command, it shipped with the NT Res kit and does the job.
Sorry for all the questions, but they often prompt the 'Aha - never thought of that' factor ;-)
HTH
Pete H
Pete...