There are a couple of things to look at:
1. Make sure that the jobs are set correctly, You can run each individual job from the jobs section. If they fail then look at the error it generates in the logs.
2. Make sure you have enough space in the drive that you are backing up to. If you run out of space calculate how many backups you can have at one time and in the maintenance job you can specify to delete backups older then xx days or xx weeks.