When I say, "Nothing's wrong," what I actually mean is, "We've been over this time and time again, and you still don't get it. By now you should know what's wrong. I'm still hurting, but I've found that talking to you only makes it worse because you can't seem to understand why this upsets me so much."
Guys, if she's obviously upset, but she says nothing's wrong, that's a clue that maybe you're not taking her as seriously you ought. Instead of trying to reason her into a better mood, try to imagine yourself in her place and see it from her point of view. Try to connect emotionally with what's bothering her.
Ladies, he can't read your mind. If he keeps trivializing your problems, then either try a different approach (preferably more objective, less emotional) to explaining it, or else understand that you're going to have to look elsewhere for empathy, support, or advice. That's one reason why we have friends, family, and church: because no one human being can take care of all our emotional needs.