1. Is it still hooked up to the computer?
Then go to the safely remove hardware icon in the quickstart bar and stop it that way.
2. Did it get this way by disconnecting it when it wasn't stopped?
Try closing i-tunes/anapod/etc and then hook it back up to the computer. Sometimes a simple thing like using a different usb port can help, especially one hooked straight into your computer rather than a hub. Restarting the computer might help as well, maybe installing an updated version of itunes will help.
3. Is it charged?
It could just be dead.
If it is charged and you can live without it for a while maybe you can wait for the battery to drain completely(likely forever).
I would hook it up to a wall charger or ipod dock which is not attached to the computer, flip the hold switch back and forth, then hold the center button(or menu and center i believe for 30gb video) in for 10+ seconds. If worse comes to worse you will have to get it serviced, or open it up and void the warranty and possibly break it(hard reset anyone?)
But there are milder options if you don't mind losing all your music, first of all the factory reset in itunes. Or maybe it will allow you to check for a software update. It might be possible to use a program such as idump (if you have windows) to backup your music before opting for the software reset.
If worst does come to worse and you don't want to send it to apple or china or wherever, then go here....at your own risk: crunch gear