Iphone alert sound not working?

My sound was working all day. Then when i tried to play a video i noticed that the volume at the bottom disappeared. So when i went to play music it also disappeared. When i press the play button no sound comes from the speaker. But when i talk to siri its perfectly mine. Also when i get text messages it vibrates instead of a sound. & no my phone is not on virbrate. I rebooted my phone, reset all my settings & i also restored my phone. Still no sound when i try to play music or receive alerts. Any advice?

This trying happened to my brother also after he watched a video. He has an iPhone 4. He gently hit the bottom part of the phone against his hand as I told him water might be he problem. It worked as good as new after.