Erectile dysfunction is basically the inability to have or maintain an erection and is usually due to an underlying physical factor. The possible reasons behind ED are:

• obesity
• diabetes
• high cholesterol
• heart condition
• high blood pressure
• testosterone imbalance

The brain plays an important role in the process that causes an erection by inducing sexual desire and releasing hormones. So, any mental blocks also contribute towards erectile dysfunction like:

• depression 
• anxiety 
• stress 
• relationship issues
• lack of communication
• performance anxiety 

Many a time it is a temporary condition, however, if the problem persists, consult your doctor to find out the underlying cause and treat it to prevent health risks.