"Not Enough Storage" Alert, bought more storage. iPAD will not reboot.n It is stuck. Held down off key for a few seconds, but it is still stuck. I have no idea what to do next. Help, please.

"Not enough storage" alert on my iPad. It gives you a choice to close message or choose settings. However, it will let me do neither. After 24 hours o rustration, I add more storage rom my pc icloud and deleted all storage. It is stuck on alert and will not reboot. I have held the of button to power off but it will not let me slide to power off. It is stuck with this alert on my iPad. Please dhelp if you can.