For the blood vessels of the penis to relax, a healthy nerve supply is needed. Therefore, conditions that affect the nerves also affect your erections.
Spinal cord injury and conditions such as Parkinson's disease, multiple sclerosis or spina bifida could potentially cause erection problems.
Other conditions that affect the health of the nerves may show up as numbness or tingling in the fingers or toes, and may indicate a problem with nerve supply in general, including to the penis.