STOP! Don't do anything more. Take the phone to a repair facility owned by your cellular service provider. They can resolve the problem. The problem (usually) is caused when either a new application or a program update has been downloaded on the phone - which has become unstable.

DO NOT attempt repairs yourself as it could make the problem worse. Just take your phone in for repairs from someone who is trained to correct the problem. It shouldn't take any more than 15 minutes to repair it.