That happened to me once before. Push the mileage reset all the way in a few times and see if that fixes it. That's what I did and it started working again. Mine was working perfectly before I took it apart. That's when I started having problems. I'm going to replace mine as soon as I can figure out which model years will fit my car.
You can also take a look here. Maybe this will help get you started:
http://instrument.articles.mbz.org/renew/
http://www.peachparts.com/shopforum/showthread.php?t=32102&page=1&pp=15&highlight=cluster
http://www.peachparts.com/shopforum/showthread.php?t=71691&page=1&pp=15&highlight=instrument+cluster+removal