Have you ruled out it being a bad - new screen/digitizer assembly? I have had power button/sleep issues caused by bad holofect communications.
The problem that are normal, is that the device boots up but then power button wont do anything but turn it off (you said you couldn't get it to turn off either though only soft boot)
Can you still try with the old screen on it and see if it still works? If it does, it points to a bad replacement screen.
Check this out for some other things you can check on the digitizer it self to see if it is missing component that cause issues like this [https://youtu.be/fdzn3ZZsPyc?t=14m39s|https://youtu.be/fdzn3ZZsPyc?t=14m39s]
Good luck!