I bought a Surface Pro 3 used and it came without a battery charger. While I was waiting for a new charger to be delivered, I ran down the battery on the Pro 3. I've since got the new charger and have had it plugged in for several hours and the tablet still won't turn back on. One thing I noticed on the new charger is that the led stays lit even when it isn't plugged in. Is there any other way to tell if the tablet is charging? Should something happen on the tablet screen when the charger is first plugged in?