Lowrance HDS 5 - screen does not always turn on

Any corrosion on the plug that goes into the unit? These are usually gold plated contacts and don't corrode. Is the power cable fused? Corrosion on the fuse ends inside the holder? Loose or corroded power cable at the spade terminal, or loose or corroded ground? Those are the most likely. Other things could be the plug goin' into the unit could be loose or the center pin loose or a loose solder joint inside the unit. What I can tell you is that the power cord that came with my Hummin'bird was junk right outta the box. Bad connection inside plastic head itself.