We recently powered down a Windows 2008 server for a weekend as the building power supply was being worked on.
Right up until this shutdown, the backups have been happily running daily every day since they were first configured.
Today, we realised that the backups haven't run since the last night before the shutdown, and when we checked the backup scheduler it said there were no backups.
Why would this have happened?
Addendum: I can't be sure that this was the first time we powered down the server since setting up the backups.
I guess, you are using Windows Server Backup tool to create multiple schedules. Check Task history in Task Scheduler > Microsoft > Backup > Microsoft-Windows-WindowsBackup.
There's an article on "Next Run Time" value of some scheduled tasks is missing after you restart a computer that is running Windows Vista or Windows Server 2008 on MS, which describes issues with scheduled backups.
Check "Next Run Time" value for the task, if necessary - apply the hotfix.