Tablet displays logo but will not charge. Please help!

Hi, my Lenovo A5500 H won't charge. It displays LENOVO logo when connected to power source but as soon as I unplug it becomes unresponsive.

I think I had drained it too much 2 weeks ago but turning it back on repeatedly.

I've tried 20 sec on/off procedure, doesn't help. I've opened it up and unplugged the battery, held power on button for 20 seconds, reconnected the battery - doesn't help.

In any methods described online it is assumed that battery holds charge; my tablet is completely unresponsive if NOT connected to power source.

I've tried connecting to computer and genuine charger and leaving overnight; nothing.

Please help find a solution or at least diagnose the issue so that I can make a decision about throwing it away - thank you!