Hi!
I have the same problem, now.
Some days ago I have formatted my drive C: and reinstalled Windows. When I tried to program my board (I use a board, that I made myself) ARDUINO program said:
avrdude: Can't find programmer id "null"
Before reinstalling Windows I have already had the same problem, and solved it somehow, but i can't remember how!
PS. Sory, if there are some mistakes in my post- English is not my native language. :-[