for LCD touch screen problem ,sometimes it is also possible the plug is not connected correctly (misalignment) ,this would cause the touch screen to be not sensitive ,not working at all .or even generate heats to iPhone itself.

please check below video for the situation:

if this happens ,try this trick to see if it works :

"When reconnecting the digitizer cable, do not press the center of the connector. Press one end of the connector, then press the opposite end. Pressing in the center of the connector can bend the
component and cause digitizer damage."

because most of time . you don't even know that there's misalignment .

find below link for more info :

iPhone screen replacement -- case 5 connecting & removing connector error