Alley Cat,
Thank you very much for helping. Yes it is the old silver Apple TV1. It's a great little product (I have an Apple TV2 at my other house).
Most likely I have installed OS Lion and have not used the Apple TV since the install.
So, the Apple TV is working on my TV screen. The menu is up. No problem. It is connected to my network. But, when I try to find my shared photos, it says I need to connect to my computer. it gives me the 5 digit code. Normally, I would go to the computer, see APPLE TV on the shared devices list and then pair them up. At this point, the iMac is not seeing the Apple TV at all. I've tried turning bluetooth on and off. I've tried going into Sharing. None of this does anything to help the Mac see the Apple TV.