MY ADVENT TV CR1473A, OPENED WITH A BLANK BLUE SCREEN AND A SMALL FIGURE OF A LOCK IN THE UPPER LEFT SIDE OF THE SCREEN. THERE WAS THE NUMBER 7 IN THE MIDDLE OF THE LOCK.

Check the remote control for its infra-red emission. Check it with fresh batteries. Check by pressing all the buttons on it; and see whether all of it generates infrared signal while pressing. If it is found OK, check and replace the infrared sensor inside the TV. If you wish to get some details; check the site linked here. It has details about how to check a remote control; by one among the post. Surf the site with patience. Pull up older posts. http://electronicshelponline.blogspot.com/ If the remote control is found OK; check and replace the infra-red sensor inside the TV. Contact any service technician.