Try adjusting the the hood bump stop, little rubber piece(s) that determine the close height of the hood. If it is too far down, sometimes hood won't pop up. I had to raise mine, and I seem to remember a few others complaining about the same thing.
+1 - I had this problem initially as well, and tom4bren showed me how to adjust it. Super easy, just like adjusting the feet on table legs to level the table.