I've tried different things, nothing helped.
However, I did run some diagnostics mentioned here:
https://help.ubuntu.com/community/GraphicsTroubleshootingProcedure
Among other things there's a line saying:
[ 2.363541] [drm:r600_dma_ring_test [radeon]] ERROR radeon: ring 3 test failed (0xCAFEDEAD)
[ 2.363545] radeon 0000:01:00.0: disabling GPU acceleration
It is the same error I get when booting the system and it goes to black screen. I found a similar issue described here:
So, I would like to try changing grub settings, but can't enter recovery mode. When during startup I choose the option with "recovery mode" in the name, the computer goes to a screen with some artifacts and stops booting:
Any ideas how to get past that?