Yes thoose guys are 100% correct.
if you have a blue screen after replacing a screen ore removing the shield from thoose connectors it is most of the times that one screw.
i replaced a screen also and when i wanted to start up again i got a blue screen and it kept in hanging in the apple logo.
I tried to restore the Phone including DFU and all kind of other things the told me on the internet but no luck.
And then i read the post of the screws and so i pulled out all four screws and yes i made the mistake also.
I was Lucky because my PCB was not toast and now i have a good working iPhone 5S again.