Sorry to be so blunt, but this is an add to the information file, if you will....No porn. If that was the case I would at least have an answer.
Does he masturbate at all?
If he doesn't, to check on the depths of the ED, would you encourage him to try it, and see if he gets erect?
Sorry again, to be so blunt, a bit crass perhaps.
But the test may yield good info. Or if you've already tried, never mind.