Iphone 5s screen replacement problem

[Reaper22]

Hi, I'm looking for help regarding an Iphone screen replacement problem. I recently replaced the screen assembly and digitiser on my iPhone 5s, something I've done successfully numerous times on other 5s' as well as on my own. Once I had the screen installed I booted up the phone to confirm the screen was working okay and that there was no loose connections before putting on any of the plates or covers. Everything worked perfectly so I turned the iPhone off again and proceeded to put everything back together fully. Once the iPhone was back together I tried booting it up again however this time the screen lit up with the apple logo for 3 seconds before going dark and staying in this state. I've tried resetting the iPhone putting it into recovery mode etc etc but nothing has worked. I've tried connecting it to my iTunes account but it can't seem to take the phone out of recovery mode. I've double and triple checked all connections so there is nothing wrong there. I also refitted the old screen to make sure the new one wasn't faulty as only the digitiser was smashed but the same thing happened with that screen. The only thing I can think of is that the grounding sticker has lost its stickiness so it may not be grounding correctly however I do not think this would be the issue? Any help or advice would be greatly appreciated, thanks and sorry about the length of this.