Did you already try to reset your device by holding the sleep and home button for about 10sec, until the Apple logo comes back again? You will not lose data doing a reset.
If this does not help, set it up as new device, without using the latest backup afterwards.
Also try to plug your headphone jack in and out a couple of times. Could be that the phone is stuck in headset mode.
Message was edited by: Ingo2711