apple watch series 2 display black but watch shows connected to phone

apple watch series 2 display black but watch shows connected to phone. Will reboot, displays apple logo however display works only a few seconds then goes black; not long enough tp unlock. It seems all functions are working except display. Have checked settings - no to Voice Over, no to Screen Curtain, display set at 70 seconds. Haven't done a reset since it may not come back or I won't be able to see.