There is a touchscreen all-in-one PC in the main room that we use for Spotify (and it has an attached label printer for name tags).
To get the sound working, make sure the hi-fi is on (if the red light is lit next to 'Standby', then push it to turn standby off). Next, make sure the PC is playing music (i.e. it isn't paused) then press the 'Source' button until you hear audio.
With the current hi-fi we're using you won't see anything change on the little LED screen as it's broken. We might replace it, but it generally works.