No sound from Sky Box is a fairly common problem can be caused by a number of reasons, however there is usually an easy fix.
It sounds obvious but it’s always worth double checking the the mute button on the remote has not been accidentally pressed.
It is possible that the Scart or HDMI connector (the cables which connects your Sky box to your TV) has come loose again causing no sound to be heard. It’s also worth double-checking the cables are correctly and securely plugged in to both the TV and Sky Box inputs.