Why wont camstudio work?

Whenever I try to record something with camstudio, when I click stop and save the video I just took with it, it shows up but doesnt show an accual video. It worked on my second try, but ive done about 5 video's since it worked and none of the five worked.

Try re downloading it or if your play World of Warcraft, Fate, Rune scape or any other full screen games putt it on windows.