It's my first time to download and use mkv video files. I used KMPlayer and I downloaded Lost S4 in 720p resolution. When I maximized the window in my 22" HD monitor (1680x1050), the video went blank. I can view it in its standard window (720p). And when I moved the window to my second monitor (17", 1280x1024), I can watch the video in maximized form. Is this a problem of my video card? That it can't output HD video greater than 720p?

Also, I can't hear the center channel (the sounds of the voices) of the video. Maybe I only have a 4.1 speaker, and my onboard sound is 5.1. How can I force the voice to output to my 2 front speakers? If I choose only the left or right channel on the player, I can hear the voice. But if I select both channels, no voice can be heard. So if I choose only the left or the right channel, does this mean I'm hearing only mono sound?