central button does not respond anymore

The center button is part of the click wheel assembly. follow these instructions iPod 4th Generation or Photo Front Panel Replacement Once you get to the last page you see the wheel in the housing. It is attached with some double sided tape/glue. There is a notch from where the click wheel cable exits from the wheel, lift the cable slightly and start prying the wheel up with a spudger or small screw driver. It may take some time to loosen it but it does work (I just replaced two of those) Once it is loose you can just remove it and place a new wheel. It will only fit one way due to some notches in the housing. It is not a very difficult job, but take your time and familiarize yourself with the repair manual.The parts are available on ebay and are not to expensive. http://cgi.ebay.com/Apple-Ipod-4th-Gen-C... Also while you go that route, throw in a new battery :) good luck