Whats up with my phone, This only started to happen yesterday?

Quick back-story yes its been dropped a couple of times and yes the screen is crack and it was only yesterday that this problem started.

What happened was it was hooked up to my school laptop and was doing assignments went to edpuzzle and it for some reason just started glitching out. and now its like the photo below. and its got these really small horizontal black lines going across the screen and its just really concerning (and bugging ) me at the moment. please help and tell me whats going on