Volume not working on TV

Question

I have a 37 inch Vizio HDTV and recently when my boys unplugged their Playstation from the TV and the volume does not work when we try to watch TV. BUT the volume will still work with the playstation on and also the DVD. I have been through everything I can think of and unplugged everything and reset everything that is possible. But still no volume available when the TV is on...HELP!