HELP! My dog is severely afraid of going down the stairs!

Help! Please! My dog is very afriad of going down our hardwood stairs.  He has slipped multiple times and he is a very big dog so I cannot carry him.  I have always caught him and guided him down, but it is a very scary situation for him.  However, whenever we try to keep him downstairs for the night, he also seems scared to be alone.  He will cry and cry.  We tried to just let him cry for a while but he cried for about 45 minutes at which point he started howling.  After that other dogs in the neighborhood began to hear him and started to bark and howl with him!  For a while, he was very good about coming down.  It would only take about five minutes to bring him down.  But lately it has gotten very bad.  I have had to try for 30-45 minutes.  Sometimes I am unsuccessful and I have to wait a couple of hours until he has to go bathroom very, veyr badly then he will eventually make it down the stairs with another ten minutes of coaxing.  Does anyone have any advice for what I can do?