Monitor On Hdmi Won´t Play Sound Only From Streaming Video!?

this is really messed up. been using two samsung monitors for over a year now, one on vga the other on hdmi both connected to my acer. sound comes from the one on the hdmi. always watched a lot of video on it - from megavideo, youtube, netflix, stuff downloaded on vlc player, etc. etc. now suddenly the sound from streaming video, no matter the website, just won´t play. with the hdmi connected, it doesn´t play sound from streaming but it does from files played on vlc; with hdmi disconnected,

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