It looks like a bad connection somewhere.
Have you tried jiggling the cables / connectors to see if you can make the right channel cut out / cut back in?
Are you listening to the amp and is the analog setup working? I doubt it’s the computer…
I don’t know what “Cinch” connectors you have, but if you can swap the left & right channels that might give a clue.
Do you have something else (and the appropriate cables/adapters) that you can plug into the computer? You can try a CD/DVD player, the audio outputs from your TV etc.