Running a desktop with 3 monitors, Asus Sabertooth Z 97 motherboard, I7-4790 CPU, NVidia GEForce GT 730 graphics solution, 24 GB RAM. Was running until this last update the 5.14 kernel. Plasma desktop. Encrypted file system. Downloaded the update and re booted, GRUB loaded, selected the OS, went to a screen with a blinking cursor. Nothing more. Ctrl+alt+F2 into a command prompt to check lightdm status and found that instead of lightdm, gdm was enabled on the machine. Checked gdm status and all appeared ok. Rebooted to the same blinking cursor. Ctl+Alt+F2 again, tried “startx” , got"no screens found". Downgraded both the kernel and the headers to lts, tried rebooting into 5.10 and same result. Blinking cursor but able to log in Ctl+Alt+F2. Disabled sddm, lightdm and gdm to give me the option of using startx from the CLI until this troubleshooting was finished. With all 3 DM’s disabled I go straight to the login screen from GRUB. Startx yields no screensfound. Ran nvidia-xconfig which theoretically generates a new xorg.conf file. Rebooted. No screens found. From there sudoed nvidia-installer-dkms - t said couldnt find a suitable driver for the graphics card use the --force option and follow further instructions. Checked this page
https://www.nvidia.com/en-us/drivers/unix/
and what appears to be the latest, the 470.82.00 driver lists that it supports the GT 730. But nvidia-installer-dkms wouldnt play. So yay’ed the 470 xx driver package. DKMS tried installing that until it spotted a conflict between NVidia 470xx utils and nvidia utils at which point it kacked. Says that nvidia utils are required by nvidia dkms which earlier in the program it said that dkms would be replaced by nvidia 470xx. What a crock. inxi -Gxxc0 says the nvidia driver is loaded. As a total aside enabling lightdm, starting lightdm takes me right back to the blinking cursor I get just after selecting the OS in GRUB. So at this point not really sure what to do next. Any suggestions appreciated. Many thanks. Lots of great info here, I searched through a number of threads before posting this. I would like to add that this is the first update that has broken Endeavour since I have been running it. Thanks.
Sorry to hear about your issue, but this is the thread (and solution) you’re looking for:
Hi Scotty
Many kind thanks for this excellent thread… Will report back on how the resolution goes. You are most excellent !
Scotty
Works! Most excellent. Solved.
Thanks very much. I must have used the wrong search terms that I did not find the thread you directed me to.
I have a question. I disabled all of the display managers-lightdm, gdm and sddm to be able to get to the login prompt without more keystrokes when I was troubleshooting this. When I updated–or downgraded as the case may be, the NVidia packages… I was abloe to startx after a reboot. When I did X started but I did not get the desktop, only a couple of terminal windows on the center of the 3 monitors. That was interesting. I re enabled gdm (which the system was using before) then started it and it took me to the normal user name/login screen/prompt one gets when things work normally. I was under the impression that gdm, sddm and lightdm all were packages that only provided the space between Grub selection and desktop i.e. that these packages only function was to get one to the user name/password parts of the system and from there on everything was handled by X. It appears that I was wrong in my assumption, that whichever one of these is selected, it also is running in conjunction with X during normal system operations. So the display manager has an ongoing function when the system is operating not just between grub and the desktop, yes? I here to fore thought after entering the password and hitting return that the display manager’s job was done. Now it appears it still performs a vital function hand in hand with X…
Again many thanks. Great learning experience this!
And a later edit. Answered my question with some DuckduckGoing. Thanks again Scotty.
Display managers like gdm and sddm essentially do exactly what you think they do. I use Gnome, so in my case when I just quickly see what processes I have running, I have a little small process called gdm-x-session. It’s not using any CPU power and barely any memory, but from what I am only assuming at the moment, it’s there is the reserves until I lock or logout of my desktop, then it’ll work it’s magic again so to speak. This is by no means a technical take on either display manager, just my own whimsical observation at 2 in the morning 
Thanks very much Scotty. Its interesting. I have the desktop in question set to remember the last session at logout and use it to among other things monitor sun weather its effect on the earth (with the new sunspot cycle we are starting going off so far with a bang)…so when I restarted after the driver magic you pointed me to I got the single monitor as before. I logged in and started X…all three monitors back lights came on but got the two terminals in the center monitor. Had the mouse but the monitor order was wrong like the Xconf file had been destroyed–which I thought it was considering I ran nvidia-xconf… but when I enabled and restarted gdm it took me to the login screen and then to the remembered desktop. Rebooted again and completely back to normal… Its too late to play with it now but I think I am going to go back and disable gdm and reboot tomorrow to see what effects I might see doing that…
I deeply appreciate your kind help and explanations.
Regards
No worries man, glad your system is back in working order! Carry on using your system how best you like to, just be sure to not go staring at the sun too often now!
Next time you buy a graphics card, think hard about whether that is going to be Nvidya.
Hi Kresimir
Funny you should mention that. After I was running again last night I spent some time trying to find laptops with AMD solutions on the CPU and graphics rather than Nvidia. My laptop died recently. Have been in the market for one I can do both some simple coding on, do photo processing (requirement for a good color gamut screen) and some other creative things… Somewhat difficult to try to find something like that that will run Linux because its not getting Windoze…and something thats out of the Intel/AMD camp without spending $3000. I have recently lived through both on Endeavor and other distros, AMD problems. Couple of years ago we got Specter/Meltdown although that affects AMD as well but from what I understand to a lesser extent than Intel…so I agree completely. Any recommendations for a laptop would be appreciated but maybe I should start another thread for that–
Thanks for the great suggestion. I have been thinking along these lines as well.
Regards
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