A woman who is unable to achieve orgasm by any means is suffering from anorgasmia.(Male anograsmia is dealt with, to a certain extent, in the node retarded ejaculation) This inability may be due to any, or a combination, of several causes both physical and psychological.

If the woman has never achieved an orgasm, her problem is described as Primary Anorgasmia. Between 10 and 15% woman are thought to suffer this condition. Secondary Anorgasmia describes the condition of a woman who has climaxed in the past but cannot do so at present. Surveys generally suggest that somewhere between 33% and 50% of women experience orgasm infrequently and are dissatisfied with how often they reach orgasm. 

Physical Causes:

Some drugs, including alcohol, can inhibit sexual response including orgasm.

Some diseases, such as multiple sclerosis, diabetic neuropathy, and spinal cord injury can interfere with the nerves in the pelvis, inhibiting sexual response.

The most traumatic cause of anorgasmia is infibulation - a form of FGM where the clitoris (the organ which makes female orgasms possible) is excised, along with most of the vulval tissue.
Other physical causes of anorgasmia in women include congenital defects including malformation of the clitoris, vulva or vaginal vestibule

Hormonal imbalances, such as an abnormally low testosterone level may contribute to anorgasmia by reducing the libido to such an extent that neither emotional or physical arousal, nor orgasm are possible.

Psychological Causes:

As mentioned previously, anorgasmia may have psychological causes. If a girl has been exposed to severe 'moral' conditioning, teaching her that sex, sexuality and female bodies are dirty or a cause for shame she may well reach adulthood without the ability to experience orgasm.

Likewise, people who have been the victims of sexual attack may discover that their sexual response has been damaged as a result of this experience leaving them either temporarily or permanently unable to experience orgasm.  

Sadness in one's relationship, dissatisfaction within marriage or boredom or monotony in a woman's sex life can also lead to  a lowering of libido and to anorgasmia.  When enjoyment does not accompany sex, it can become a chore rather than a mutually satisfying, playful, and intimate experience. When anorgasmia persists, sexual desire usually declines, sexual frequency wanes, and this may create resentments and conflicts in the relationship.

Treatments:

The first step in the treatment of anorgasmia, primary or secondary, is to attempt to determine the cause.

For some people, such as those who have experienced infibulation, or those with neural breakdown due to spinal injuries will never be able to reach orgasm. Women with congenital defects may require surgery.

There is a much better chance of achieving a full sexual response in women whose anorgasmia is psychological in nature. Education on the ways the body reaches orgasm can be helpful. Some people with primary anorgasmia are given a masturbation plan to follow in their attempts to reach a sexual climax. Once the first orgasm has occurred it is far easier for the woman to achieve the next and subsequent orgasms.