Norton Back Up fails

When I try to back up to an external hard drive or a DVD, the program runs through up to 7500 files and then fails with a statement that 2 files could not be backed up.  I get a message that I should turn of all other programs and then restart back up.  I have gone to msconfig and turned off all programs that I can find.  This does not help.  I have tried rebooting to safe mode.  Norton won't run.  In the case with backing to a DVD, I get a message that the disk has failed and I need to use a new unused disk.  That is what I was using.  I have gone through a whole tray of new disks with the same result..  I need help.

Thanks for the suggestion; however, I have 232 GB free on my C drive, and I am not backing up to that drive.  I am backing up to a 4.7 GB DVD in the E drive.  I have also tried backing to my external hard drive that has about 20GB free.

When I try to back up to an external hard drive or a DVD, the program runs through up to 7500 files and then fails with a statement that 2 files could not be backed up.  I get a message that I should turn of all other programs and then restart back up.  I have gone to msconfig and turned off all programs that I can find.  This does not help.  I have tried rebooting to safe mode.  Norton won't run.  In the case with backing to a DVD, I get a message that the disk has failed and I need to use a new unused disk.  That is what I was using.  I have gone through a whole tray of new disks with the same result..  I need help.