I tripped while carrying my LCD monitor to its new location, and pressed hard on the screen with my fingers as I tried to steady myself.  ( yes, famous for being the clumsy oaf ).  The LCD crystals leaked from their little cells, and I now see a black blotch across my screen when I switch it on and connect it to my computer.   So that's another way to change how  you see what's on your monitor.

Eternal Hobbyist