How to putt under 40?

I am an avid golfer Victoria, British Columbia. My golf game is suffering from a complete lack of total skill on the green. Yesterday I hosted a corporate event for my office and I shot 40+ putts. It was very embarring. I often have 4 putts and sometimes the occasional 5 putt. I recently switched to a reverse or cross handed grip in 2009. It has not helped. I continually hit 40 putts in 18 holes. Sometimes I loose my temper and feel like throwing my putter in the ocean. My son has tried to help me on to learn to putt on several occasions, but he will longer play with me because it is embarring to watch me putt. I would sincerely appreciate any help and/or instructional videos on how to putt under 40.