I found and old Sharpe LC TV, in great condition. The onscreen menu works perfectly, and I was able to locate the FACTORY RESET, and reset the TV, after which I attached my, COX Cable wire, my ROKU box, and my laptop computer into the HD inputs, using an HD wire but no picture came on? No matter what I tried. Oddly, the ROKU logo and sound were visible when I first plugged in the box, but also followed with a dark screen. HELP. Why is the signal not getting to the television? My cable, ROKU and laptop all work perfectly and connect to my VISIO TV? Someone said it could be my memory board? Can someone guide me through the process of seeing if there is a block in the setting from the previous owner? I would hate to throw it back to the curb. Model #LC52SB57UN