My iPhone 4S has gone silent

Hello.

i have had my iPhone 4S for about a month.

in the last coupla days it has started giving me notifications without sounds, not "clicking" when i type, not playing the sound in Youtube (not even showing a volume slider....pic attacehed at the bottom),

it is not switched to silent, and i can still flick it to silent which still shows the "silent" symbol on screen, and in turn the "unmuted" symbol when i switch back.

I also cannot change affect the volume with the side buttons.

If i got to "Settings" / "Sounds", i can hear the ringtone when i adjust the "Ringers and Alerts" slider, so i know the internal speak is working, but doesn't affect my problem when i go back to the home screen....still totall silence upon incoming calls/texts/emails.

i really don't expect this to be happening to a brand new phone, especially one that cost me £200.00 in-store with my renewed 2 year contract.

Can anyone help me? I don't believe i am alone here.

thanks....Richie x