Did it happen suddenly or very rapidly over a short period of time, or was it a very gradual process? If it was gradual, what were the first signs you noticed? Did it start taking longer and require more foreplay to get an erection? Did you ever have surprises where you tried to have sex and and expected to, but suddenly could not do so?
How did your wife or girlfriend at the time react when you started having those kinds of problems but were not impotent yet? Were there times when you could still have an erection, but needed her to perform some physical stimulation of your penis in order to succeed? Was she willing to spend more time in foreplay and to take a more active role in stimulating your penis? Did you and her realize you were becomming impotent at the time?