Mike, some also just like to be grumpy (like this well known Smurf
) but it's also possible that he currently suffer depression (if he was not always like that). I am not a doctor but i once read that a lack of testosterone in men can cause such behavior (as you mention he have no drive toward women it might be a cause).
Don't do like him thinking he will not open to you, he accept to see you and to talk to you, that is the hardest part. You don't need to be direct with him, you may talk about you to him and then ask him how it compare to himself, from time to time you may get a glimpse to his hidden wish (he can't be sad about life and the world without having an idealized view of the world inside him to compare, this view is his dreams).
You can pray and you can force him into action. For example you can start a project by yourself or do a sport, community work and ask him to join from time to time. If he is not violent when drunk, you can take him with beers around a camp fire (this open everybody like a book usually).
It's really good of you to try to help him, but at one point you can bring the horse to the fountain but can't force him to drink. I hope you won't be depress yourself if bringing him up to life fail. At least you really identified the solution: making him see all of the good things that are within his reach. Even if nothing of what you do seem to have an effect, it's perhaps just him not wanting you to know you made progress, inside him i sure think he appreciate the effort you are putting on him. You and him remind me of Ricky Gervais and Karl Pilkington in that TV show: link
(Ricky send his grumpy friend on trips, literally to discover the "wonders" of the world and get out of his closed mind and comfort zone)