First off, I have already seen this question. It's almost identical the the problem I'm having, except that my second monitor never worked to begin with. I tried the solution suggested in the comments, but it had no effect.
I have two monitors plugged into a SAPPHIRE PULSE Radeon RX 580 8GD5 graphics card. One uses the DVI port and the other is plugged in with an HDMI cable. Both moniters work during BIOS display GRUB properly, and work for my Windows 10 partition, but only the one plugged into the DVI port shows up when I'm running Ubuntu. I have installed the latest amdgpu drivers. I'm not a Linux guru by any stretch of the imagination. I've looked at a bunch of different threads and tried a lot of different things but nothing has worked. Here's the outputs for some commands:
josh@jrevans-desktop:~$ lspci -nnk | grep -i vga -A3 | grep 'in use'
Kernel driver in use: amdgpu
josh@jrevans-desktop:~$ sudo lshw -c video
*-display
description: VGA compatible controller
product: Ellesmere [Radeon RX 470/480/570/570X/580/580X]
vendor: Advanced Micro Devices, Inc. [AMD/ATI]
physical id: 0
bus info: pci@0000:09:00.0
version: e7
width: 64 bits
clock: 33MHz
capabilities: pm pciexpress msi vga_controller bus_master cap_list rom
configuration: driver=amdgpu latency=0
resources: irq:121 memory:e0000000-efffffff memory:f0000000-f01fffff ioport:e000(size=256) memory:fe900000-fe93ffff memory:c0000-dffff
josh@jrevans-desktop:~$ xrandr
Screen 0: minimum 320 x 200, current 1600 x 900, maximum 16384 x 16384
DisplayPort-0 disconnected (normal left inverted right x axis y axis)
DisplayPort-1 disconnected (normal left inverted right x axis y axis)
HDMI-A-0 disconnected (normal left inverted right x axis y axis)
HDMI-A-1 disconnected (normal left inverted right x axis y axis)
DVI-D-0 connected primary 1600x900+0+0 (normal left inverted right x axis y axis) 443mm x 249mm
1600x900 59.98*+
1280x1024 75.02 60.02
1440x900 59.98
1280x800 59.98
1152x864 75.00
1280x720 59.98
1024x768 75.03 60.00
800x600 75.00 60.32
640x480 75.00 59.94
720x400 70.08
josh@jrevans-desktop:~$ lspci -nnk |& awk -v n='[0300]' 'p&&/^\S/{p=0}!p{p=index($0,n)}p'
09:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere [Radeon RX 470/480/570/570X/580/580X] [1002:67df] (rev e7)
Subsystem: Sapphire Technology Limited Sapphire Radeon RX 580 Pulse 8GB [1da2:e353]
Kernel driver in use: amdgpu
Kernel modules: amdgpu
09:00.1 Audio device [0403]: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere [Radeon RX 580] [1002:aaf0]
Subsystem: Sapphire Technology Limited Ellesmere [Radeon RX 580] [1da2:aaf0]
Kernel driver in use: snd_hda_intel
Kernel modules: snd_hda_intel
0a:00.0 Non-Essential Instrumentation [1300]: Advanced Micro Devices, Inc. [AMD] Device [1022:145a]
Subsystem: Advanced Micro Devices, Inc. [AMD] Device [1022:145a]
0a:00.2 Encryption controller [1080]: Advanced Micro Devices, Inc. [AMD] Family 17h (Models 00h-0fh) Platform Security Processor [1022:1456]
Subsystem: Advanced Micro Devices, Inc. [AMD] Family 17h (Models 00h-0fh) Platform Security Processor [1022:1456]
Kernel driver in use: ccp
Kernel modules: ccp
0a:00.3 USB controller [0c03]: Advanced Micro Devices, Inc. [AMD] USB 3.0 Host controller [1022:145f]
Subsystem: Gigabyte Technology Co., Ltd USB 3.0 Host controller [1458:5007]
Kernel driver in use: xhci_hcd
0b:00.0 Non-Essential Instrumentation [1300]: Advanced Micro Devices, Inc. [AMD] Device [1022:1455]
Subsystem: Advanced Micro Devices, Inc. [AMD] Device [1022:1455]
0b:00.2 SATA controller [0106]: Advanced Micro Devices, Inc. [AMD] FCH SATA Controller [AHCI mode] [1022:7901] (rev 51)
Subsystem: Gigabyte Technology Co., Ltd FCH SATA Controller [AHCI mode] [1458:b002]
Kernel driver in use: ahci
Kernel modules: ahci
0b:00.3 Audio device [0403]: Advanced Micro Devices, Inc. [AMD] Family 17h (Models 00h-0fh) HD Audio Controller [1022:1457]
Subsystem: Gigabyte Technology Co., Ltd Family 17h (Models 00h-0fh) HD Audio Controller [1458:a0cc]
Kernel driver in use: snd_hda_intel
Kernel modules: snd_hda_intel
