The DIY section has tons of information on kegerators. Check there.
At a glance, you'll need: new tubing, Ball or pin lock connectors for the type of corny keg you use, and a good cleaning session. I'd even go so far as to disassemble the tower a little and soak the parts in PBW n sanitizer. after that, check your regulator, and make sure there's CO2 in the tank, and you should be good to go.