My iPhone 4 sound Doesent work?

It only work with earphones. I have not dropped the phone or done anything to it. It happened for the first time today when I was watching a video on YouTube and the sound suddenly stoped.

Could have gotten wet. Happened to my sister's. Have it checked out or upgrade.

It's possible that the earphone jack is stuck. IPhone 4S had an issue with headphone jacks. Try inserting and removing the jack until you get sound while playing a song or video.