It seems you used the .run file installer to install over the ubuntu packaged driver. That creates a mess.
Uninstall the .run file install using the --uninstall parameter to the .run file.
Delete the /etc/X11/xorg.conf you created with the .run file installer.
Then purge all of previously installed packaged nvidia drivers. sudo apt purge nvidia* libnvidia*
Then install the nvidia driver through ubuntus “Additional Drivers”.
Make sure the nouveau driver is blacklisted (if you don’t know how, search the web). - Shutdown
Also you got “gpu has fallen of the bus” messages. Reseat the GPU (pull it out and put it back in) in the PCI slot and check the power cabling.
Start the computer…