First of all you need to know if the problem it's only with the speakers or is a software issue.
Try to go to settings and look for the volume settings to be sure everything is on the top level.
- If that is checked and it's still not working then try to use a headphones to check if works that way.
-I am assuming you already tried to reset the tablet then if nothing works, the problem for sure will be hardware, now you need to open the tablet and look for a lose connection with the speakers inside.