First make sure it has a charge. Plug it in and if it shows that it is charging, leave it for a few hours. Then come back and try turning it on.
If you plug it in and it doesn't actually show it is charging, then you need to check both the cord and the battery to see if either is needing replacing. Yes I know the batteries are harder to get to. This is why, if the device is still under warranty, you should "not" open it up, but contact your provider or the manufacturer.