Same thing happened to my galaxy tab 3. I fixed it by carefully removing the back cover (not for the faint of heart) and disconnecting the battery for a few minutes. The white battery connector has 6 wires going to it and lifts straight up and off 6 itty bitty pins. After a few minutes pop the battery connector back on. Don’t put the back cover back on yet. Plug the charger in and charge the tablet for 30 minutes. Then try turning the tablet on. It should turn on as usual. Carefully replace the back cover and make sure to snap the edges down all around. Fully charge the tablet. Don’t forget to re-enter your wifi passwords and reset the date and time or you won’t be able to access the web. Good luck.