I have a Gigabyte H87-HD3 desktop with AMD Radeon HD 7850. I installed Ubuntu 20.04 (completely erasing Windows 7) a few days ago and I still can't get it to start without "nomodeset", because of purple screen before login (I see the Ubuntu logo for 1-2sec and then plain purple, no logos, no errors)
Esc and Crt+Alt+Del: nothing happens. Ctr+Alt+F4: Terminal starts and asks for login and password. I provide them and it seems that Ubuntu runs normally, but without any GUI, only Terminal.
I searched extensively for a solution and I tried installing mesa ppa and oibaf ppa for drivers, but it still didn't work, although I made sure everything is installed, updated and upgraded. I also tried to modify the GRUB, adding "radeon.modeset=0" (and (...)=1) after "quiet splash" and still purple screen. I also tried installing proprietary drivers only to find they are discontinued. This is the info I think may help:
biller25@Biller:~$ sudo lshw -c video
*-display UNCLAIMED
description: VGA compatible controller
product: Pitcairn PRO [Radeon HD 7850 / R7 265 / R9 270 1024SP]
vendor: Advanced Micro Devices, Inc. [AMD/ATI]
physical id: 0
bus info: pci@0000:01:00.0
version: 00
width: 64 bits
clock: 33MHz
capabilities: pm pciexpress msi vga_controller bus_master cap_list
configuration: latency=0
resources: memory:c0000000-cfffffff memory:d0000000-d003ffff ioport:e000(size=256) memory:c0000-dffff
*-display UNCLAIMED
description: VGA compatible controller
product: Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller
vendor: Intel Corporation
physical id: 2
bus info: pci@0000:00:02.0
version: 06
width: 64 bits
clock: 33MHz
capabilities: msi pm vga_controller bus_master cap_list
configuration: latency=0
resources: memory:d0400000-d07fffff memory:b0000000-bfffffff ioport:f000(size=64)
and
biller25@Biller:~$ inxi -G
Graphics: Device-1: Intel Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics driver: N/A
Device-2: AMD Pitcairn PRO [Radeon HD 7850 / R7 265 / R9 270 1024SP] driver: N/A
Display: x11 server: X.Org 1.20.11 driver: ati,fbdev unloaded: modesetting,radeon,vesa
resolution: 1024x768~76Hz
OpenGL: renderer: llvmpipe (LLVM 13.0.0 256 bits)
v: 4.5 Mesa 22.0.0-devel (git-c4d9041 2021-11-06 focal-oibaf-ppa)
I don't really understand it and there is also a great chance I messed up a lot of things in my attempt to fix the purple screen. I hope someone can help.
Edit: This is the neofetch result, after the reinstallation of gdm* and gnome*
biller25@Biller:~$ neofetch
.-/+oossssoo+/-. biller25@Biller
`:+ssssssssssssssssss+:` ---------------
-+ssssssssssssssssssyyssss+- OS: Ubuntu 20.04.3 LTS x86_64
.ossssssssssssssssssdMMMNysssso. Host: H87-HD3
/ssssssssssshdmmNNmmyNMMMMhssssss/ Kernel: 5.11.0-38-generic
+ssssssssshmydMMMMMMMNddddyssssssss+ Uptime: 2 mins
/sssssssshNMMMyhhyyyyhmNMMMNhssssssss/ Packages: 1756 (dpkg), 8 (brew), 12
.ssssssssdMMMNhsssssssssshNMMMdssssssss. Shell: bash 5.0.17
+sssshhhyNMMNyssssssssssssyNMMMysssssss+ Resolution: 1024x768
ossyNMMMNyMMhsssssssssssssshmmmhssssssso DE: GNOME
ossyNMMMNyMMhsssssssssssssshmmmhssssssso WM: Mutter
+sssshhhyNMMNyssssssssssssyNMMMysssssss+ WM Theme: Adwaita
.ssssssssdMMMNhsssssssssshNMMMdssssssss. Theme: Yaru [GTK2/3]
/sssssssshNMMMyhhyyyyhdNMMMNhssssssss/ Icons: Yaru [GTK2/3]
+sssssssssdmydMMMMMMMMddddyssssssss+ Terminal: gnome-terminal
/ssssssssssshdmNNNNmyNMMMMhssssss/ CPU: Intel i7-4770 (8) @ 3.900GHz
.ossssssssssssssssssdMMMNysssso. GPU: AMD ATI Radeon HD 7850 / R7 265
-+sssssssssssssssssyyyssss+- GPU: Intel HD Graphics
`:+ssssssssssssssssss+:` Memory: 1594MiB / 7837MiB
.-/+oossssoo+/-.
