Why can't I change the sound settings?

Hello,

My phone is stuck in ‘alarms only' mode for sound, and when I pull the top menu down the button simply doesn't respond. All the other options there, inc Bluetooth, brightness, hotspot etc all work fine but the sound doesn't work.

Why is this, and is there anywhere else (ive searched through sound settings and can't see anything) that I can change it to total silence or to loud?

Thanks

Cait