What should you do if coauthor refuses to work on paper and refuses to consent to submit it?
No, you probably can't just submit it yourself if the prof is validly a co-author. You need his permission, just as he needs yours. 

But I suggest that you let the two professors fight it out among themselves. That could result in a good result for you, and probably not a worse one. Professors sometimes don't mind behaving badly in front of students, but are less likely to with colleagues. Collegiality is still valued in most places. If it needs to get escalated, let the new advisor do it also, on your behalf.