I'm a newby to this also and I had the same problem. After reading through the forums I found this free download to fix the "codec" problem. Go to this site: http://www.codecguide.com/ scroll down the page to K-Lite Codec Pack 2.83 Full/Standard/Basic and download.
I downloaded the full version and I went back and was able to see and hear the video with no problem. Hope this helps!