What is the turning point in the book 1984 by George Orwell? Are there three turning books in the three different parts of the book?

I wouldn't say there are three different turning
points.  The main climax of the book is the point in which Julia and Winston are in
their "secret" apartment above Mr. Charrington's junk shop and they get caught by the
Thought Police.  Everything leads up to this seemingly harmless bit of Paradise and
freedom that these two characters indulge in; however, it is quite against the law and
policy of The Party (whose main purpose to gain power over its own people for the sake
of having power). 

From there, we go inside The Ministry of
Love with Winston and learn more about the Party's policies from within its confines. 
The resolution of the book, then, is the only one it could be: vaporization of
Winston.