I had exactly the same problem. I tried three different screens/lcd and none of them worked. I saw the answer from Bob who worked and unfortunately putting the phone into recovery mode and doing a restore is not necessarily and option. I would have to know the persons id and password. Should I be acquiring their credentials?
In our case the phone would just make a dink sound every few seconds and would never boot up. Holding the power and home buttons did nothing to resolve the problem.
We were able to acquire a replacement phone but never found the cause of the problem.
If did read through some forums and found where one guy retried the old screen and the phone came on and then was able to connect the new screen and it worked and seemed to solve the problem.
Share if you have had the same problem.