It has probably run down the battery - connect it to the wall charger and let it sit for at least 30 minutes, it should recover.

When it turned off due to the battery running down it also probably fixed the locked up issue.

If it locks up again, hold the Menu and Center buttons down simultaneously, until the Apple logo appears - this may take 30-60 secs.

Yes, you could do that but if your in a hurry, you can open your ipod with the ipod opening tools (can buy it on www.ifixit.com) and unplug the battery and replug it. iF it is constanly locking up, you might want to update the firmware on your classic or just reformat it. BE WARNED, doing this will take off all of your music.