Well there could be a number of issues that could have caused this I will help try to narrow it down for you.
Issue 1
Potentially if you have left the battery connected while performing the repair then you could have made a component blow. In this case micro-soldering would be the best way of fixing.
Issue 2
While you were performing the LCD replacement when you lifted up your connectors you could have accidentally damaged some of the components by prying on them with out realising some of these parts can be so small you can't really see them by eye this mistake is very common.
Issue 3
The LCD you are using could be the issue there maybe something wrong with it from the supplier. If you have a new LCD handy test it with that before hassling your supplier.
If you have a digital usb voltage meter connect your phone to it and read the display if your getting a very high reading then chances are you have a short circuit inside this can help you guesstimate the issue without even opening the device.
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