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What I find interesting are prior discussions about this. https://www.google.com/search?q=The+display+settings+could+not+be+saved.+Please+try+a+different+combination+of+display+settings.&ie=utf-8&oe=utf-8 finds the 7870 and ATI cards in general. Maybe it's time to try an Nvidia.
tl;dr -- using an hdmi splitter knocked out a separate monitor.
I'm running a Radeon 7850, and had three monitors connected and working perfectly on Win 10. One via DisplayPort, and two via DVI. I got gifted a 50" TV, and wanted to be able to use it to watch videos / play games via my computer, so I ordered an HDMI splitter so that the TV could duplicate my primary monitor. (This was necessary because my 7850 only supports 3 simultaneous monitors.)
My primary monitor was hooked up via DisplayPort. So I also got a DisplayPort -> HDMI cable, ran that to the splitter, and ran the two HDMI outs to the primary monitor and the TV. When I did this, the primary monitor and the TV looked great, with the signal successfully split -- but the other two monitors were no longer receiving signal.
After messing around with various settings and such, I eventually got one of the two monitors to run. So now I have one working solitary monitor, a working primary monitor duplicated on my TV, and a non-functional monitor. Windows detects the non-functional monitor when I run desk.cpl, but has it listed as disconnected, and when I try to enable it I get the message
"The display settings could not be saved. Please try a different combination of display settings."
I googled around and tried all the usual things -- unplugging various monitors and such. In case it's relevant, all my working monitors are 1920x1080, but the non-functional monitor is 1280x1024. The desk.cpl window won't let me change the resolution on this monitor down from the unsupported 1920x1080 after I select "extend".
Help!!!

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