After the ios9 update, the ipad worked for about 5 minutes, then it just restarted and went into the "installing update" screen with the progress bar. It stays about 1/4 of the way then just reboots, goes to the restart screen without the progress bar and then the bar appears again. It's just on a continuous loop.
Try to reset your device. This won't delete your data stored on this device.
Alternatively, you may go to Settings - General - Reset - Reset All Settings
https://support.apple.com/en-us/HT201559
If this does not help, restore your device to factory settings. Note that this will erase the data from your device.
Take a look this Apple Support article: Use iTunes to restore your iPhone, iPad, or iPod to factory settings - Apple Support.
I was able to get the ipad into recovery mode, downloaded the new updates 9.0.1 and restored my ipad through itunes and it's working now.
I Did this, restored as a new iPad both via iTunes and on iPad and it still keeps restarting, nothing seems to help. What sort of glitch is this, I have no idea. If someone has a solution please post.
I forgot to mention, it started doing this after the ios 9.1 update. It either gets stuck in a loop or if I manage to turn it off while in a loop, it restarts every once in a while, some 5-10 times a day. As far as I know, cause I don't use it 24/7 either.
I have the same problem with iPad2. After the update it restarts after going to standby. I'm not even sure when it restarts but every time I turn it on it behaves like a restart and get the message "after restart you must enter password". Getting worse as now I must reset the device to even turn it on and the battery level keeps dropping quickly. New battery? How?
After iOS9 installed, ipad mini keeps rebooting.
