• What is it?

ED the persistent inability to attain and maintain erections of sufficient rigidity for penetrative sexual intercourse. Not only men who are unable to achieve a satisfactory erection, but men who cannot maintain one long enough to either reach orgasm or satisfy their partner are suffering from erectile dysfunction.
The majority of men who suffer from ED are over 40 years of age, but this does not mean that ED does not affect many many younger men. If you are old enough to wish to maintain an erection for long enough to have an orgasm, you are old enough for ED to affect you.

Impotence includes this meaning but also has pejorative connotations 

Some of the other symptoms associated with ED are:
loss of libido
anorgasmia
premature ejaculation

Of these, only anorgasmia is easily measured by the individuals involved. Loss of libido is generally noticed on a more subconscious level, while premature ejaculation is, in many cases, quite subjective. It comes down to this. If you can achieve penetration before ejaculating, but cannot sustain it as long as you and your partner desire, you are suffering from premature ejaculation.

Many millions of men have ED to some degree, ranging from complete inability to have an erection to occasional problems. A once-off failure to perform to your own and your partner's expectations does not mean you have a serious erectile dysfunction.

  • What Causes ED?

ED has many different causes including blood flow problems, drug side effects, nerve impulse abnormalities, hormonal abnormalities, surgery, prostatitis, prostate cancer, penile trauma or scarring, and psychological causes. So it is often very difficult for an individual to discover which (or which combination) is the culprit in their own case.
Most ED does have a physical cause at root, but there is almost always a psychological component to the problem. Because ED is such a worrying thing for most men, a single erectile failure can become a mental block to the next erection, and so men can go on having psychological erectile dysfunction after the physical cause of their problem is rectified.

  • What can be done about it?
One of the best things to do if you believe you have an erectile dysfunction of more seriousness than a couple of less than satisfactory erections or an embarrassing but once or twice off case of PE is to see your doctor. Finding out what is wrong with people is what doctors are for, after all.
You may well feel embarrassed about it, but would you prefer to put up with fifteen minutes of acute embarrassment or with a lifetime of unsatisfactory sex?

When you do decide to see your doctor it is a good idea to write a letter to take with you and give to your doctor. This letter should outline your problem in some detail and include all the questions you want to ask. That way if you do succumb to embarrassment, or forget just what you wanted to say,  you will still be able to pass the paper to the doctor and let him work his way through it. Answering specific questions is much easier than making the first "I can't get it up" statement.
If he can see you have taken the trouble to write your problem down in some detail, your doctor is much more likely to take your problem seriously than if you simply mutter something about "having some trouble 'downstairs'" at him.

It's a good idea to read up on ED before you see your doctor. You should find out about different causes, treatments, and what you think the cause of your ED might be. Not only will doing this make it easy for you to understand what your doctor suggests to you, but you will have a pretty good idea if your doctor doesn't have much knowledge about ED. If he appears to know less than you do, get another doctor :)
ED isn't a very 'sexy' problem and many GPs don't know as much as one would hope about the subject, and even some urologists and endocrinologists are not well educated about it.
Some of the therapies for dealing with ED are listed below, with a little information on each one.

Constriction bands are ideally suited to men who can achieve a satisfactory erection, but cannot maintain it for a long enough time. 
A ring a whisker smaller than your erect penis fits over the penis, stopping blood leaking back into the body until the man has finished with his erection. CAUTION: This is, in effect, a tourniquet, and should not be left on for longer than 30 minutes.

Vacuum pumps
are often used by men who have trouble achieving an erection to begin with. They are often used in conjunction with constriction bands. 
The penis is placed in a tube and a hand pump sucks the air out, forcing the penis to expand and fill with blood. When a satisfactory erection is achieved, the pump cylinder is replaced by a constriction bad. Remember, don't leave a constriction band on for more than 30 minutes at a time.

Viagra
is of use to many men who have a lack of erection but no lack of libido. It works for between 60 and 70 percent of men in this position who try it.
It is best to take Viagra on an empty stomach. 
Many men report side effects when taking Viagra. The most often reported are a headache, flushed face and a stuffy nose.

Muse suppositories
are for the same group as use Viagra, but their usefulness seems to be much less, with only 3% of users reporting them to be effective.
Muse suppositories are inserted about an inch deep into the penile urethra, delivering Prostaglandin into the erectile tissues of the penis causing smooth muscle relaxation and a resulting erection
It also, apparently, "hurts like hell"

Penile injections - Caverject, Bimix and Trimix
are injected into the erectile tissues of the penis with a very fine needle. The first time this is done is at the doctor's surgery, but you are expected to learn to self inject if you plan to use this drug regularly.
CAUTION: if, after a penile injection your erection does not go away within three hours you should see a doctor at once. Priapism is extremely dangerous and can result in gangrene and amputation in extreme cases!

Penile implants
are surgically implanted erection makers, and come in two basic types: malleable implants, which allow the user to bend the penis into the desired position and angle, and inflatable implants which are pumped up by means of a control located in the scrotum behind the testis. No one can see you are using either of these implants on casual inspection.

Remember, no matter what your individual problem is, there are many many people who have had it before you, andd you should, if you are able, make contact with a support group (such as alt.support.impotence online) and share experiences with more experieced sufferers. This is a good way to avoid falling into the pit of despair, and you just may be able to throw some light onto another person's problem