How to fix iPhone 4, no sound?

I dropped my phone and smashed my iPhone 4 screen a few months ago, haven't noticed any problems apart from the screen until now. When I have headphone in sound works perfectly fine with everything. However without headphone in sound only work with incoming calls, texts and alarms. I can't play music or watch videos/music.
Anyone know how I can fix this? Please!

Is it still under warranty? Than apple will fix it for you.

if the warranty is invalid, you can find an electronics repair center. Although it may be expensive you can still get it fixed. Look up repair centers online.