Replaced front panel, last 2 screws left then screen when black!

I was finishing a front panel repair and down to the last two screws on the outside to close everything up. I clicked the home key to check for working, it was and I slide the bar across, Yea!

So I put the two remaining screws in and pulled off the front protective film and then their was a black screen with nothing. nada. black.

None of my attempts at the "top button and home key" could get anything. No response. I did a careful repair taking my time and watching a few videos before I did it myself.

So basically one minute it is working and the next its dead. I have also put it on the charger for a few hours, because it did have a low battery, but still nothing. Checked the 3 connections again, still nothing.

Any advise, fix, or next step??

Thanks-M