If you have an older iPhone and tried to update with the new iOS 9.0 update it might have backfired and won’t let you into your phone. It is frustrating as you have to restore your phone to factory settings.
I called Apple and that is really the only option. Or wait it out. But depending on how bad you need your phone that might not be the best thing.
Apple is working on 9.1 to supplement and fix the bugs in 9.0 and I was told that could be around Monday or Tuesday when it is released.
Here is a link to the Apple support site for more troubleshooting: