By not working, do you mean it does not power on, or it powers on but is not recognized by the display, or it powers on and is recognized but displays nothing, or it displays but everything looks funny
#1. Personally verify any work
not done by you. No matter how many installations they have done.
#2. Have someone verify any work
done you. No matter how many installations you have done.
If it is not powering up, I think there are two different color wires in it that need to be connected. This may have been confusing during the install.