It could be a codec issue, but its more likely something just ended up in the wrong spot somehow during installation. That article should put you on track to clear it up.
A codec is a system for compression video data, to reduce the file size. There are lots of different codecs out there, each designed for a specific purpose. Some are designed for editing, and ensure that a very high level of quality is retained. Others, such as those used by HD cameras while filming, sacrifice quality more in favor of smaller file sizes. It is important to understand theat the container that the video in, such as .mov or .avi, is completely different from the codec, and that a wide variety of codecs are available to use on a .avi file, for example.