Replaced display assembly - home button & screen don't work

I have followed the guide (Sostituzione schermo iPhone 4S) to replacing the iPhone 4S display assembly. I believe I did it correctly except for one thing (the 1.5mm screw in step 18 seems to have been stripped on the way out so it is not securely replaced).

Now the home button doesn't work (it won't depress unless I put a lot of pressure on it), and the screen doesn't work either. When I turn it on, it starts out gray and with lightly defined vertical stripes that slowly fade out, then it lightens to a brighter gray, then goes dark.

Any thoughts would be much appreciated!