Why is the sound not working in apps?

First, make sure that you check your tablets overall audio settings to make sure that sound is enabled and the volume isn't completely turned off.

When you try using the physical volume controls, does a volume status show up on the screen? If there is a " / " through the speaker icon then your tablet is stuck in mute. Try using the volume control to move the volume all the way up and then back down to toggle the mute icon.

If you don't mind doing a factory reset that would be your next step, to perform this follow the steps on How to Perform a Factory Reset. Be careful with doing this because it will wipe out all your data.

If this still doesn't work you may need to replace your headphone jack and speakers, the steps for these can be found here: Headphone Jack Replacement and Speaker Replacement.

If none of these solutions fixes the problem you may need to contact Toshiba directly.