Why won't my sanyo tv get any sound?

My sanyo tv works great, except for no sound! It forced me to pick an option on here, but the only sanyo option available is not what I own; my model number is dp50710. I don't have cable, so no cable box to plug any cords into and no antenna to pick up any local channels to see if sound works on regular channels. The only cord I have is the power cord for the tv; I also use a firestick for shows/apps and this is where the problem is…no sound on any shows! I also have it set to make sound when I click from one thing to another and that gives me no sound either. BUT, when I hooked up our Nintendo switch to the tv everything works fine-- sound included!! I don't understand what's going on! How can I get the sound to work on everything that plays on the tv??!!