iPhone 6 connects to iTunes, nothing else.

So a few days ago I was fixing my iPhone 6 screen by replacing the entire assembly. I test my screens periodically through out the process so as to minimize troubleshooting in the end in case I messed something up.

I would turn the phone on, test digi and lcd, and turned it back off by holding the power and home button (I think this might have been part of the problem).

Well, right before I was about to put the metal plate cover back on everything worked fine. So I turned the phone off and put the plate on. But now the phone won't show anything on the screen, digi didn't work, no sound, no calls, no vibration. Weirdly enough the phone still connects to itunes, goes to DFU mode, even connects to bluetooth and can do a full iOS restore without any errors. Unfortunately, even after the reset, the rest of the phone still doesn't work.

Now before you go on saying its the "long screw problem", I can assure you that wasn't the issue. I've worked as a repair technician in the past for phones and can usually do these in my sleep. Also the phone was a personal phone and never came into contact with water.

Does anyone have any idea what the issue could be and/or can push me towards the right direction of at least troubleshooting the problem?