I am 72 years old, all of sudden I no longer have erections at all. When I do which is not very often, the erection is so weak. I exercise regularly, walk about 21 miles/week. Try to eat right. I have tried Viagra, it use to work for me, no more again. I have also tried Viagra, sometimes it works, some times, it doesn t. What is the problem and what can I do to grt things working again? My wife is concerned