I know this is an old thread but Im posting my solution to this problem as I could not find any on google either. I had the exact issue described and found that my heavy desk was sitting on and crimping the power cord to the monitor causing the problem. I suggest anyone with this issue inspect their power cord and/or swap it out as a troubleshooting step.
I had already tried swapping input cables, gpu drivers, and display ports between my cards.
This was on 2 GTX 550Ti in SLI with 3 monitors.
Hope this helps someone!