When people ask me "How do I record my computer screen using CamStudio", I reply "It's easy, do not use CamStudio!" Throughout the years, I have had far too many bad experiences with CamStudio. Sometimes CamStudio works OK. However, when things go wrong, they can go really wrong. Sometimes CamStudio freezes, and cannot be shutdown. A complete restart of the computer is required. Sometimes I was able to record a video, but the .AVI file was totally corrupted, and wouldn't play at one. Once after experiencing an issue with CamStudio, Windows would no longer boot! I had to boot into Safe Mode and then restore my computer to a previous restore point. Long story short, it just aint' worth the hassle.
Use Monosnap instead.