Has anything changed with your set up. If not have you tried a different cable. Have you tried capturing to a different computer. This kind of thing needs a Sherlock Holmes style investigation to eliminate things one at a time. It could be a faulty socket on the camera to a new piece of software on the computer. If you can try different scenarios to eliminate things one by one eventually you may find the fault. OR if you have the money take your camera to a repair shop and have them look it over.