Honestly thought by now this would be fixed, but it's the same as ever. I have a desktop with an Asus Vanguard B85 motherboard, and 3 monitors. 2 of the monitors are BenQ GW2255s on DVI and DVI to DP adapater, and 1 is just an old 19" Lenovo monitor on plain old VGA cable.
Ever since I attached the 2nd BenQ monitor the Intel driver has absolutely refused to recognize all 3 at once. The monitors all come on as Windows is starting, but then the driver loads and poof it pretends it isn't there anymore. "No Signal Detected". Now for Windows 8.1 this was less of a problem, because if I disabled the driver and then re-enabled it the 3rd monitor would be recognized and I'd be all set until the next time I restart the computer. Not ideal but workable.
However with Windows 10 it's pure crap. Not only does disabling/enabling the driver no longer work, but when I try it the Lenovo monitor starts flashing base colors and I have to manually power off the computer to get it back. I've tried upgrading to Windows 10 3 times now and every time I have to downgrade immediately back to 8.1 just to be able to use the computer properly.
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