Because it was not compatible between PC and TV. (PC Windows 8.1 64-bit). If the computer has been running and I turned on the TV, the monitor of the PC was black, but recovered, however, automatically change the font size on the PC. I pulled the cord to the computer but back out, the font was back to normal on the PC. I then get borrowed cable from a friend an oil Bach HTML and there were not the problems indicated on. So the fault lies properly in the cable, which is not sufficiently shielded.