Mayo Clinic’s overview regarding erectile dysfunction (ED) provides a good source of information. ED refers to the inability to get and keep an erection firm enough for sex (impotence). Most men older than 60 experience some degree of erectile dysfunction. Erectile dysfunction differs from other male sexual dysfunctions, including premature ejaculation; Peyronie’s disease, which causes penile curvature; and priapism, which is a painful and prolonged erection. Researchers believe that for most men, erectile dysfunction results from physical (organic) not psychological problems. These medical problems usually are related to the blood supply system in the penis. Men with cardiovascular risk factors, including high blood pressure (hypertension), high cholesterol, smoking, diabetes and family history of early heart disease, are at particular risk of erectile dysfunction. Additional risks are prior pelvic surgery or pelvic radiation for cancer, medications, coronary artery disease and peripheral vascular disease.
I am sure each person (man) who experiences ED have different underlying conditions; therefore, it is probably that you consult a physician regarding underlying causes. For more information see link below: