Clicking on the Start Record button is the final step in the DVD creation process and it requires that step 1, "Select burner" and step 2, "Select source" have been completed. Look at the text just above the Record button, and if is displays "Press 'Prepare' to initialize the media," the DVD has not been initialized.
In section 1, make sure the correct DVD burner is selected, that the DVD media that the drive supports is in the drive, and then
In section 2, video has to be playing in the preview window before the press the prepare button. If You can click the Start Record button.