I'm sorry to hear this. Have you tried changing the type of cables that you're using?
I get the bouncing box with check signal cable display port, when my monitor is on and working fine and the only way to rid myself of it at times is to bring up the monitor menu.. I am running dual monitors both U28d590 on a GTX 980. Any idea how I can fix this issue? Oh and this only happens on the main monitor, and the box also appears while the monitor is going into sleep mode..