When Characters Won't Cooperate

The romance is gone—actually, it never was. What do you do when the two main characters in your romantic suspense refuse to go beyond "like"? I've tried forcing them, but the scenes are artificial and flat. Somehow they got to be friends, but the chemistry isn't there. No zing. Also, this book is too short. And I don't like the ending I had planned. I'm not sure where it all went wrong, but it