Norton Ghost 15.0

I bought a new computer with Windows 7.  I installed a second hard drive to house my backups.  I defined the backup th Norton Ghost 15 and ran the first backup successfully.  I set a schedule for M,W,F at 3am but the backups never run.  But when I click on Manage Backups / Run Now, the backup works.  Why wont it backup automatically according to my schedule?