Sound buttons and mute switch not working

My iPhone 4 has no sounds through the phone speaker except when I play music. It works fine through a dock or bluetooth in my car.
Also, the side 'sound buttons' do not work. ie - when I switch the mute switch to either on or off (and it becomes orange) nothing shows on the screen, also when I push the volume buttons up or down, nothing comes up on the screen.

I have tried: turning it on and off, resetting it, cleaning the charging port with a dry brush, checking the settings to make sure it should be playing sounds, inserting head phones a few times.
I have recently updated to the new 6.1 iOS update, but it was doing this before I updated it.

I can't think of anything notable that happened when it started doing this a few days ago. Seems random...

Also, my iPhone has had sound problems before (speaker crackling and not working) but the side buttons still registered on the screen, and also I could fix it by charging it.
Anybody got any handy hints?? Cheers.