My iPhone 4 will not ring, but plays music out loud? Help!

Heyy!
So my iPhone is playing up… The deal is that it wont ring or play music during games or anything like that, but will play music out loud! When i switch the little mute button on the side, it changes nothing and it doesn't even work as usually it shows the little bell on the screen when you slide the mute button, it no longer does this… Also the volume buttons on the side do nothing. Tried cleaning it, I'm wondering if its something I've done App or software wise, or if its mechanical?
Any help would be much appreciated!

Check if "Do not disturb" is on

Best help you can obtain at the shop where you bought it.