I tried the method of holding for 30 seconds etc, but it didn’t work. Then I saw your comment Tia about holding he on/off button down for 5 minutes and tried that. I’m not sure if it is working, but the charging icon flashes on and off now, and it showed 0% at one point. Fingers crossed.
An update to my previous comment. What I did didn’t seem to work. The screen kept flashing, and sometimes a message would come up “Android Downloading. Don’t turn off the source” and one time I got the recovery menu. But all the time the screen just kept flashing. I would also see the charging icon, but it always said 0%!
But, the flashing slowly reduced in frequency, so I kept trying the “hold down the start button and volume up for 30 seconds…..” method, and when I had a few free minutes I would try holding down just the power button for as long as I could be bothered (several minutes).
Finally, the charging icon stayed on for a few seconds, so I left it alone while I went to the dentist. When I came back, maybe an hour later, I pressed the power button once which brought up the charging icon, and to my surprise, it showed 1%. It was charging……
So, I don’t know what did it in the end, but my “dead” Samsung tablet is now working. As another commenter said, I will not let it fully discharge again.