When you are unable to keep or get an erection for intercourse, the problem that comes at this time is called erectile dysfunction. It is most common in men between the ages of 40 and 70, although it can affect younger men to a lesser extent. It is often associated with high blood pressure, obesity, diabetes and high cholesterol. This can sometimes be the cause of an underlying medical condition. However, most men may sometimes fail to maintain or achieve an erection. It can usually be the result of excessive alcohol, stress, smoking and fatigue. Sometimes men may have difficulty in maintaining an erection due to anxiety or psychological issues.