Same with me. Just replaced my screen as I should. Phone starts but screen is black. If I remove the back cover I can see some light inside the phone. Edit: Just did the whole process all over and put back my old "not-so-good" screen. It works just like before. In other words, I did not make any mistake in my assembly. The new screen doesn't work.
So now I got it to work. What I did was to take out the new power button and replace it with the old original one and now it worked. In other words it was the cable and the mechanism under the button that was broken but when the original button was replaced with a new one, the new button becme the problem. Going back to the old button solved it.
Now I solved my problem. A few weeks ago I got a new power button - thinking this was the reason my power button wouldn't click. Changing the button didn't do anything so I bought the Power and Sensor cable and tried to fix my phone today. However still no "click" regardless of how I put the power button. I then got this idea to try with the old button that I had unnecessarily replaced... " and voila...springiness." Works great regardless of which way I put the power button. So don't buy the power button to fix "no click". And if you did - don't use it, it's crap.
Doesn't work for me regardless of what way I put the button. The guide shows the bracket hanging all the way down and that was also the way the button was in my phone when opened it. I have tried it both ways. No springiness or any function of the button despite new button and new cable. Guess I just have to live with no power button.