Make sure all the connections to the motherboard are securely in place, there may be times when some of the cables are partly connected and some are not, leading it to not function properly. Also this tends to happen if you tighten the bracket above the cables too tightly not giving the cables a secure fit into the logic board. Also it can be easy to damage the connectors when not being careful, leading the components to breaking or not functioning properly. I always recommend turning off the device and taking out battery before repair, just to be cautious and to help not accidentally fry a component while during operation. It can also occur when people purchase off-brand screens, which tend to be the really cheap priced LCD/digitzer. So make sure you purchased the screen from a reliable company/brand. Hope this helps the situation. If 4 screens are all having a difficult time, it may be the component on the motherboard.