I have an 42LD550 LG tv and get a NO SIGNAL when trying to connect to a Roku or Apple tv box thru HDMI port. The Roku worked at one time on HDMI but stopped one day. I have switched ports and cables. The Roku works with RGA cables. At first I thought the Roku HDMI was blown but now that the Apple tv fails to connect I suspect cheap cables or blown HDMI ports on the tv. How could all 4 ports go bad? Is there a way to test the cables or ports?