Impotence.

Sex is a part of productive life, and like hunger, is also a basic instinct. In some males, this 'act' becomes difficult to perform.
Impotence is the failure of a man to achieve or maintain an erection, and is more common in older men. Sometimes this term 'impotence' is also used when a man can have an erection but cannot ejaculate semen.
Causes
Psychological
The most common reason for a man failing to get an erection is psychological. He might be overtired, over­stressed, worried or just desperately lacking self-confidence, or it may be due to excessive demands or criticism of his performance by his partner.
Any type of hostility, anger or resentment towards his partner, constant fear of making a woman pregnant, guilt perhaps about an affair or any other negative feeling about sex, can also be the factors.
Physical
Sometimes 'impotence' can be traced back to certain health problems like diabetes, severe depression, or severe reaction to any drug. Excessive alcohol drinking or cigarette smoking can also lead to impotence.
Signs & Symptoms
There are varied types of impotence:
If failing to get an erection is a rare and short-lived problem, it is normal.
But when it becomes a long drawn problem after a period of normal sexual function, it has to be attended to urgently.
There are a few men who right from young age have difficulty in achieving an erection enough to sustain intercourse.
Herbal Medicines
Reassurance: A sympathetic partner can contribute a lot in helping a man overcome this problem. Similarly the man should assure his partner that he still very much wants to show and receive affection.
Despite all these, if a couple cannot work it out together, it is worth consulting a doctor.
If a physical cause is found, suitable medical treatment should be taken.
Garlic: Garlic is a powerful aphrodisiac and regular use keeps a man fit and fertile. In Ayurvedic medicine it has been described as poor man's nectar. It works wonderfully in all types of impotence, resulting from over­indulgence and nervous exhaustion.
5 to 6 garlic cloves should be crushed having removed the outer coverings and added to a glass of milk, boiled and reduced to ½ glass. Then it should be filtered, required sugar should be added and taken twice a day in two equal doses.
Dried dates also produce aphrodisiac action. These should be taken daily as a supplement.
Black raisins are also useful.
Ayurvedic Remedies
Ashwagandha Lehyam is the common medicine for this disorder. It should be taken internally in the dosage of 10 to 15 gm twice a day with a cup of warm milk.
Musli Pakam taken 2.5 to 5gm once or twice daily with warm milk gives good results.
Ashwagandharishta 1 to 2 ounces twice daily after meals with equal quantity of water is a useful remedy.
Kapikacchu is a drug of choice but should be taken under medical supervision.
There are many other powerful medicines in Ayurveda for the treatment of impotence. These are to be taken under Ayurvedic physician's supervision, as such they are not listed here.
Do's & Don'ts
Massage: An energetic massage all over the body is highly useful in this condition. Sri Gopala Tailam, an Ayurvedic medicated oil should be applied over the hip and pelvic region, before massage.
Yoga: Certain yogasanas like sarvangasana and dhanurasana are indicated.