iPhone won't turn on after software update

Last night I went to update my iPhone 4S to the latest iOS 7. I went to sleep while it was updating and it was charging and when I woke up it wasn't on and it kept vibrating every few seconds when it was charging. I tried to turn it on, then I tried to restart it and held the home and sleep buttons for 20 seconds. I tried connecting it to iTunes and iTunes won't detect a device. Any help??