Thanks for your quick reply.
1. I was out of town when my wife experienced this problem so I can't say that the unit was not moved or nudged. It is in a large cabinet on a very secure shelf so I don't think that would have caused the problem.
2. This unit has a six CD tray in it with an open/ close button instead of a eject button. I can't hear anything when you try to open the tray. None of the other buttons give any audible or visual indication that the system is trying to operate either.
I removed the player from the shelf and as I did so the player tipped and a CD fell out. So, I shook it a couple of times and ended up with six CD's on the floor.
I plugged it back in and it is working.
Thanks for your input. It looks like it was a jammed CD.