In most cases, people who have the rotation issue just need to unlock the rotation lock. If you are not sure how to do this, I have written up a tutorial [http://vkrepair.com/how-to-rotate-screen-on-iphone/|here].
Since you said that you have unlocked it and it does not work, it just might be a faulty sensor. However, it seems that you have opened up the iPhone, double check that you are putting the screws in the right places as the magnetic screws can cause an interference if placed in the wrong spot!