It might be due to a break in the thin blue cable. Mine had a death grip on the RCA connector, and after some insertion/removals (maybe once pulling by the cable,) the solder connection broke. I was going to solder it back, but I thought that cable was worth probably only 10 cents.

It shoudl not be due to the power cable, but since that blue cable is probably only single shielded, you'll never know.

You could try that cable as a substitute for a composite cable in your video system. If the picture is bad, then you know it is the cable.