Touch screen doing odd things after a screen replacement..

dropped my phone bout 6 months ago, screen caved in eventually and the touch screen stopped working. got the screen and lcd replaced three days ago. now my touch screen is doing strange things. (note that this only happens if i lock my phone and leave it be for a while or if i have multiple apps open..) it's not responding, opening apps, calling people, typing random gibberish.. the likes. what could be wrong? a hardware issue? or just something not installed properly?