Did you do Main Menu>>Sounds & Display>>>Orientation and click on the square for the green arrow check to appear?
This question has come up many times, including a thread created by me. The home screen does not flip unless you get an Open Home app.
Mine flipped right out of the box, no programs need or affected it. It does however flip only when turned to the left (like you were opening the keyboard, nothing hapeens when flipping to the right.