as I can't add comment to your question, just wanted to thank you for providingUnchecking Compositing in the answer: unchecking "Compositing" on Render's "Post Processing"Properties editor > Render tab > Post Processing rollout did solve the problem. side
Side note: you can go to the compositing nodes in the Node editor (or choose "Compositing" Layoutscreen layout) and change/remove the Source Movie to remove video from render. :)