Exporting a Video in Quicktime in OSX Lion Shows only Audio

Is anyone having the same problem? I'm trying to export a video in OSX Lion to either 480, 720 or 1080 but it only exports the audio file. After the export the file is in .mov format but when I play it, the file shows nothing, only an audio is played. Before I have a Lion update, I can export videos just fine. How can I resolve this issue?
