Sounds silly, but if you really want to orgasim the more you think about doing it the harder it is to do! That's from a femal perspective. Both of you should try not to focus on it so much and eventually it will happen. Try different positions, maybe she needs something at a different angle. If it feels good to her and feels like the orgasm "gets stuck" it's probably because of all the anticipation and 'nerves' and it just stops. That can happen. Maybe you are going slower when she's about to. That can stop it midways too.

Hope this helps. =)

There isn't an Orgasm Button on a woman. Female sexual response is very complex and as Lil Scorpio alluded it's hugely based on comfort and arousal.

I'd start with foreplay, spend a little more time turning her on, be patient when you touch her, let her body lead the pace that you move in. If a woman is aroused enough you can bring her to orgasm with a deep kiss.

Also age can be a factor. If your girlfriend is under teh age of 20 its not all the uncommon for a woman to not yet be orgasmic, even if she's managed to reach orgasm through masturbation it may be a while before she's leared what she needs to do to get there with a partner.

Patience!

I have noticed that being tense can effect a female orgasm.
When I first started seeing my new freind, we had sex, I never came, and she didnt, I didnt coz I thought she was uncomfortable with me, we talked about it and she was worried because her ex boyfriend was lurking around.

Now that she has moved,she is more relaxed, and orgasms all the time!

Comfort is the key.