If you are still having problems have you tried changing the Audio out option or rebooting the 360 by turning the power off and on.
You could also try a factory reset if the reboot doesn't work
You are given 2 options, select the keep recordings option.
Keep Recordings
Format Disk
Keep Recordings, means you won't lose your recordings and any planned recordings or series links you've set up, but you will have to sign into your apps such as iPlayer, Prime, Netflix and ITVX again, also Match frame rate and Standby power consumption will go back to their default settings if you have changed them.