Why the apple support sad face?

I have these ipods. Not sure if it's they are 5th generation video or the classic 5.5. Non working, so I took them apart to try to fix. How can you tell the difference in them. I've replaced batteries, lcd screens headphone jacks and hard drives. The hard drives all had clicking noise so I got a new 80 gb drive. It says it is only compatible with a 5.5 but it doesn't work in any that I tried. Maybe I need the 60 gb drive. They all have the thick back cover. All I get is the apple sad face on two of them while the computer says the other one is corrupted. Not sure what to do next. Are all parts interchangeable? If not I need to find out what model they are. Could it be the motherboard? Any help would be appreciated.

Jeff