I definitely agree that time is going to be a big factor here. I think that both of you are just nervous right now, and that's exactly what is happening here - when he's trying to 'get it up' he's just getting too nervous and that's getting in the way.
Yes, you could definitely try change of scenery - from trying at night, shutting off the lights or trying his place. Maybe even try leading yourself and see how he reacts.
But in all honesty I think you just need to talk this out. Okay, here I go, some of this is NSFW either:
While I understand that it's weird to think about, you two need to talk about what turns you on. Fantasies, anything. Maybe he doesn't know what you like and that's part of what's making him nervous. He might be fearful that if he does something that you don't like you'll leave or something.
You definitely need to talk to one another about this, but do not blame him. That makes things ... horrible. You will get no sex.
Anyway:
To signal him that you'd like to talk you might schedule a time. Watch your posture, too. Make sure you're not standing with your legs spread and your hands on your hips. It's a little intimidating, you know?
That way he isn't freaked. You do not have serious love conversations with a guy when he's watching the game or when the last thing he seems to want to do is talk.
Definitely speak calmly to him and tell him that you value his opinion, because some guys say that in times where their girlfriends 'need to talk' they feel like they can't get any words in edgewise.
So here is an 'I' statement, which might sound a little funky to you, but I swear it works. It gives a person a chance to put themselves in your shoes and vice versa because that way you aren't directly blaming them (which is a huge no-no):
'I feel (feeling) when (this happens / happened) because I want (something)'
Example: I feel angry when you make me do my homework because I want to go outside and play.
They can be modified, of course, but make sure to stay along the same lines. Here's the reflection version of it:
'[I heard you say] You feel (feeling) when (this happened / I did this) because you want (something.) Is that correct?'
Example:
I heard you say you feel afraid when I don't exercise because you want me to stay healthy. Is that correct?
So heres what you do not do as a reference:
"You always make me wash the dishes,"
"You're such a lazy pig, you never help out,"
and "I wish you could do something nice for once in your life."
And that is all. I really hope I helped. <3
-Infinity