Toshiba Power and/or Sound goes out for no reason

I'm having a problem with my Toshiba 57H84 that is approx 27 months old. Almost every time there is a power outage, however brief, the picture and sound would go out ... sometimes for days. Then one day we'd turn it on and everything was fine. Recently, the sound has been going out ... for no apparent reason. One minute it's working and we're watching tv, the next minute ....no sound! And it might stay this way for several days. Then we'll turn it and and voila!  all is fine. Any ideas???  It's driving us crazy!!