my iPad's battery died and now it won't charge or turn on?

If the battery was empty then it can take about 15 minutes of charging before it will respond. If you've charged it for longer than that then have you tried a soft-reset to see if that gets it to boot up ? Press and hold both the sleep and home buttons for about 10 to 15 seconds, after which the Apple logo should hopefully appear and it will boot up - you won't lose any content, it's the iPad equivalent of a reboot.

Are you using the iPad whilst charging it, and are you using the iPad's own charger (and iPhone or iPod charger aren't as powerful) ?