The male sex hormone testosterone also plays a major role both in sexual desire and in being able to have an erection. You may be worried or stressed, so your brain is not alert to the signals of the testosterone hormone. Or your body may not be able to make testosterone or may make so little that your brain doesn't get the message. You may have nerve damage. If the nerves to the penis are damaged, they may not be able to send signals.
Nerve damage can also limit blood flow.
This can prevent an erection. Psychological impotence often starts suddenly. It can be caused by fear, worry, anger, or sadness. It often focuses on one person or event. Men hear so much about impotence and diabetes that they may expect it to happen.