Prolonged blank screen during setup of new cable box

While setting up the new cable box that Xfinity sent me (unsolicited), I connected all cables to the back of the box and turned on with the new remote. On the TV, after the welcome message, it asked if I would like the onscreen instructions spoken as well as written in the screen. I answered no. Next the screen went blank but occasionally, there would be three blinking dots to tell me something was still happening. Then the three dots stopped and the screen remained blank but the TV was still on for the next 20+ minutes, and counting.