Are you sure it charged?

When you plug the power in, it automatically powers the device up to a point, and displays a graphic that shows the battery charging, or an indication that the battery is fully charged.
Once it is fully charged, you can hold down the power button (the one towards the middle, not the outside as I saw on one website's illustration!) for about 3 or 4 seconds, and it will boot.

If it does not power on and boot up, pull the battery out, then re-install it and try again.
I bought two of these, and one of them had a problem 2 or 3 times where it locked up black and would not do a thing until I popped the battery out and back in.