Thanks for the bug report. Your kernel log is saying that the Nvidia driver is not cleanly installed, so please use the 'Additional Drivers' app to remove it, then reboot, then reinstall it using the same app.
Please also consider installing a newer Ubuntu release. The one you have will reach end of standard support next year. ** Package changed: xorg (Ubuntu) => nvidia-graphics-drivers-535 (Ubuntu) ** Changed in: nvidia-graphics-drivers-535 (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2068537 Title: screen does not go blank after the configured period To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers-535/+bug/2068537/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs