Have you tired to restore the iPod when you plug it back in. Often it needs to be restored to get the new parts working.

If it is showing the same symptoms as before even with restoring it probably means that the logic board is bad and you will need a new logic board.

As to the loss of functionality it is possible that some of the cables got slightly disconnected. When I have problems like this with the iPods I usually take it back apart and disconnect the reconnect all of the cables just to make sure they were making a good connection.