iphone 4s problem after screen replacement

[diggler007]

hello people, I was wondering if you can help me ?
This is my first post here so not sure how this works! Anyway I have recently changed over a broken screen on a 4s , initially the replacement worked but without the touch, so on inspection I realised I made a rookie mistake and had damaged the ribbon while installing! I ordered a new one and was very careful to install the new screen. when I turned on the phone it vibrated once but no screen at all. when I plugged it in the laptop both the phone and computer recognised connection. I did notice the first time after installing the second screen the logic board became quite hot to about 5 minutes. I stripped the phone back down to make sure that I hadn't missed anything.
Next I tried to test the first screen (the one with the broken ribbon that at least came on) but now that wont even come on. I have checked all the connectors/ribbons/screws and they're all good. please can someone help which other options I have.
P.s I read on a forum that it could be a problem with the OS on the phone not compatible with the "new" screen and that I should update the software on the phone. This left me confused as how to go about it ,when I have no screen input available to navigate. when I plug into laptop it says that I need to unlock my phone from handset before connection. Thank you in advance for any help