Iphone 4s frozen on icloud storage alert?

My iphone 4s randomly had an alert pop up saying
"not enough storage. This iphone can't be backed up because there's not enough i could storage available. You can manage your storage in settings." it won't let me click the close button or settings on the alert, it stay frozen. I can't shut it off or answer calls or anything. Its brand new so its pissing me off.

Have you tried restarting it?

Hold the power button until it does