Hello, I have a problem with my ZenPad z500m tablet, it was lying around for a while and now it won't turn on. I tried to hold the power button 60-90 sec, power button and volume + and -, disconnected the battery. The battery has a voltage of 3.8V. The computer detects it as a MediaTrek device. The screen is black there is no loading icon. I used several regular chargers and fast charging ones. What could have happened, it wasn't dropped or anything, it just lay unused for a long time.