IPhone 4 has no sound

There's no sound playing music and going on YouTube but there's sound on my alarm clock and ppl calling

You should try turning up the volume. Basically there are different volumes for media, ringtone, and alarms, so you have to turn up the volume in YouTube app to turn up the media volume. And if it's not working then well it's an iPhone wtf you expect. Get a htc one or galaxy s4.