I hate to say it, but that was the symptom when my Sling Adapter croaked. No red LED, no matter which USB port I plugged it into on my 722k. The replacement from Dish fired right up when it was connected.
I'd let it cool down if it's been plugged in for awhile and see if that makes any difference. Also, I'd unplug any other USB devices from your Hopper to see if that makes a difference.
Good luck!