What are you trying to "back up"??
Windows only?? Your data only? Both? C drive only?
Is your personal data on the C drive or do you have it separated onto a D drive?
I seriously doubt Windows Backup is supposed to reboot when finished.
I'd consider two things:
1: Using something other than Windows built-in backup to make an image file of the C partition--something like Acronis or Macrium Reflect. That would "back up" the C drive and anything it might contain.
2: Backing up personal data folders (as opposed to Windows itself) separately, without using an image. There are many apps for this, many of them free. Again, the built-in Windows tool is not particularly well-suited for this.
Windows Backup "works", but is cranky, non-intuitive, and not the leading application for the required tasks.