Windows Movie Maker Help?

I tried to make a video with WMM but halfway through it, the clips I use just go black. I try to import the clips again but it says: "...cannot be imported because the codec required to play the file is not installed on your computer. If you have already tried to download and install the codec, close and restart Windows Movie Maker, and then try to import the file again." The clips were recorded with Hypercam if that helps.