DVR recording

Last night I recorded a movie. When I went to watch it The picture got very dark. I switched back to tv and the picture got completely dark in the center of the picture. I unplugged the cable at the wall to reboot box. I got the picture back but when tried to watch recorded movie the same thin happened. I finally rebooted again and erased movie. What could cause this. I hope it isn't a sign that the DVR is getting bad.