I have two G5 Powermac used for video editing. We import narration from a DAT to the computers through the optical input in the back of the machines. We noticed yesterday that one machine was not receiving a signal. After some analysis, it appears the problem may be the actual connection, because the G5 that is receiving the signal has red light or glow coming from the optical connections and the other G5 no longer has a red glow coming from the input and output connections. Has anyone had a similar problem or failure and are there any maintenence measures I can attempt before taking the machine into an Apple service dealer?