It is doubly frustrating for a man when he can't get or maintain a firm enough erection to make love.
Not only does he feel unfulfilled sexually but it is so maddening to know you want to make love, know you desire your partner, but find yourself unable to control the crucial bit of your body.
It's even worse when your partner feels very threatened by your not making love to her and starts accusing you of not loving her or of having an affair.
So one of the first steps you have to take to resolve this problem is to be honest with your partner.
I know it's hard for a man to admit he's experiencing erection problems but the overwhelming majority of women are very understanding - in fact, they are often relieved to discover that's what the problem is.
Sharing this with your partner will also have the effect of relieving some of your anxiety - and that in itself will help since anxiety alone can cause, or certainly contribute to erection problems.
Most cases of temporary erection difficulties are simply cleared up if you and your partner agree that you won't try to have intercourse for a while.
That absolutely does not mean that you give up all the other ways of making love - kissing, cuddling, caressing, doing everything loving, arousing and satisfying you feel like doing.
Massage is a good way to get that loving closeness, and stimulate your hormones and physical responsiveness. The only thing to avoid is attempting intercourse itself.
After a few days, or weeks, you should find that one time you have intercourse easily just because you weren't worrying about it.
If you're a man without a regular partner you may wonder how you can help yourself with this problem. I often hear from men who are avoiding all relationships for fear of failure. The answer is to enjoy as much masturbation as you feel like.
Just follow your fancy. Try allowing your arousal to subside and then build it up again. When you do meet a partner with whom sex seems likely, confide in her.
Most women will be very sympathetic about this problem as long as you explain, and an affectionate couple can share plenty of sexual pleasure without needing a rock-hard erection. In fact, most women reach orgasm through stimulation other than intercourse.
Although most cases of temporary impotence are psychologically based, keeping the body in reasonably good working order helps keep us ticking over well sexually, too.
Drinking too much alcohol lessens sexual responsiveness, both at the time (the notorious brewer's droop) and generally.
Three pints of beer or six single measures of spirits or small glasses of wine are as much as a man's body can cope with healthily in a day. Cut down if you're regularly drinking more than that and always have a couple of alcohol-free days a week.
Smoking has been realised to be an important cause of loss of sex drive and impotence in men. Smoking and unhealthy diet can both cause circulation problems which affect the blood supply to the crucial parts.
The first thing that many top specialists now recommend to people with such sexual problems, particularly if they are 40 or over, is to stop smoking and follow a healthy, high-fibre, low-fat diet. Regular exercise can also benefit your sexual well-being.
Be careful though about excessive cycling, either on an exercise bike or a real one with a hard narrow saddle.
This can damage the main artery to the penis, which in turn causes problems with erections.
Sexual problems are often also linked with anxiety. If you have been suffering from a lot of tension or worry it will help you recover your sexual responsiveness if you can learn to relax more out of bed as well as in it.
If you write to me I can send you my free leaflet on how to relieve stress.
If you feel your relationship is not close enough for you to begin loving and caressing one another as suggested, then that may be the problem causing the sexual failure.
Unresolved bitterness and unhappiness very often show up in sexual difficulties.
You may be subconsciously punishing your partner. If you can't sort out what are the real problems in your relationship by talking about it calmly between you, then make an appointment to see a counsellor.
Now it can happen that, in spite of taking the emphasis off intercourse, and in spite of lots of loving and caressing, a man still can't manage to make love.
If you have been suffering from this problem for three months or more then you should see your GP to check whether there is a medical problem.
There have been considerable advances in treating this problem when it has a physical or hormonal cause, and seeing the doctor is important because erection difficulties can be an indicator of heart problems, for example.
You can also see a specialist at your local genito-urinary clinic - it's where they treat sexual infections but don't let that put you off benefiting from their expertise in this area.
What sorts of treatments are on offer? Viagra is the best known. It helps blood flow to the penis and seems to work in about 70 per cent of cases, whether the cause is physical or psychological, though it may not be so effective long-term if difficulties in your relationship are affecting your sex life.
There are worries about side-effects, such as heart attacks, especially if over-used, and it’s obviously not suitable for some men, such as those with serious heart problems.
While Viagra is still the best known, there are other drugs such as Uprima and Cialis, which can be more suitable than Viagra for some men. Cialis, for example, can now be prescribed in 36-hour and daily formulations, so you can choose to take one to cover the weekend, or a daily pill so you can always rely on being “up for it”.
A man still needs sexual stimulation and the desire to make love.
You can also talk to your doctor about other options. If you have been impotent for a prolonged period, treatment with the hormone testosterone might give your body the "kick-start" it needs to get back into action.
More and more is being understood now about how our body chemistry affects our sexual responsiveness.
However, hormones aren't a magic potion. Hormone treatment will only work if your hormone levels are the problem - though it can certainly be combined effectively with counselling or other talking-it through therapy. You can ask for a blood test to check your hormone levels.
Your doctor or a specialist can also instruct you in how to inject your penis with a drug that produces an erection. If your impotence has a physical cause, is not bound up with problems in your relationship, and you and your partner are happy about your producing erections with injections, this method may suit you.
Vacuum devices are also on the market but are clumsy to use, and rings which fit around the base of the penis to aid erection are available through your GP or specialist.
Gadgets, pills and potions are often useless or even harmful. Do look for help via your doctor.
What it is important to realise about even reputable treatments is that they will never be the answer if the real problem lies in your relationship. I would strongly recommend that as the most promising place to start, as well as checking with your GP to see if medical treatment would help or perhaps a change of medication.
This is important, even if you find the idea of talking to your GP about sex problems embarrassing, as erection difficulties can be an indicator of heath problems.
Illnesses affecting nerve tissue, such as some cases of diabetes, can damage the nerves involved in causing erection. Circulation problems and some drugs, such as steroids, diuretics and those used to treat high blood-pressure problems, can make a firm erection difficult. Pain and infections can obviously damp down sex drive, as can depression and some of the drugs used for treating it.