marriage counselling. get her in to it to sort out why she married you and if she actually wants to stay married to you. Best that you get to know the answers without fighting in order to sort through them one way or the other or this will destroy you both if it's not talked through with a professional to keep things under control.

Meanwhile, I would suggest you give up even thinking about sex. Just enjoy company and good times with her. Do nice things for her and take her out for dinner, buy her flowers. Tell her how much you love her and tell her why... without wanting a sexual "reward". Forget sex for a while until you learn some communication and really, please go to a good counselor together. A marriage without sex can't survive but there is no way you can expect her to give it when she feels cold about it. You have to find out why together... she may not even know herself.