https://www.ifixit.com/Answers/View/172833/Why+won%27t+my+tablet+produce+sound
Following the instructions in the link above fixed my problem. I reset my tablet, and as soon as the screen went dark, I pressed the volume up, and held it until it finished reseting. Then I was able to turn up the volume from all the way down, to a reasonable level about half way up, which is much louder than I've ever been able to set it before.