My tab does not turn on?

I would first suggest removing the back casing from the tablet to gain access to the battery connection on the motherboard. Then disconnect the battery from its connection on the motherboard. Let the battery sit disconnected for a few minutes then plug the battery connector back into the motherboard. Then see if it will now charge or turn back on normally. I do not know exactly why this works, but this has helped bring back many Samsung tablets I've seen that appear to be lifeless. I assume its an issue with battery calibration software used by Samsung or something along those lines, which disconnecting the battery may reset. You can follow the beginning of this guide to assist in disconnecting and reconnecting the battery. 三星 盖乐世 Tab A 电池更换

If that does not work there may be another issue such as a faulty battery, charge port, or something else causing the issue.