ms backup

Once in the Task Scheduler, select Backup from the Application view. Then choose the desired frequency of the backup. Select the time, days, and so on. When finished, press the Finish button but go into the Advanced Properties. Check all of the settings to ensure that the Backup will run.

Good luck.

The only way I have seen this fail (Assuming the clock in the PC is correct) is if there is another task running that prevents Backup from running until the start timer in Backup runs out.
Obviously, check the above.
Regards, Chris