Hello,
I have a similar problem.
Have a Aorus RX580 8GB works fine, drivers and radeon software all installs and works fine.
Connected to main monitor BenQ GL2450H with a DIV-D to HDMI cable and works fine.
Problem comes when i connect the second monitor a Dell E207WPF (winodws cannot see this but Radeon software can) using a HDMI to DIV-D cable.
When i start up i get the ASUS motherboard load screen and the windows logo appears but then when it should load the windows password screen both screens just go blank.
Have used both monitors individually with both cables from the HDMI and DIV-D socket on the GPU and they work fine.
I just cant get them to work together.
The RX580 card has only been used about 5/6 months, it has been put in this machine to replace a failing GTX770 which was about 6 years old and ran 2 screens with no issues at all. I really hope the AMD card is not failing already.
Any help would be really good.
Rob.