Gray stripe when playing dvd

After inserting a dvd that was apparently slightly warped into my laptop vibration was quite strong and the video had a gray stripe along the bottom side of the video screen (width about 1/4 th of the total screen width) and slightly blury colors. Removing the dvd and playing a vidoe that was saved on the HDD this problem persisted. Rebooting let me play the saved video without problem but as soon as I used a dvd in the dvd drive the problem was back for both playing dvd and saved video. So after rebooting I can play saved videos but no dvd without this problem. VCDs & music plays fine. Un- & reinstalling video programs did not help. There are no scratches on the drive/laser unit in the dvd drive.