Your JournalErrors.txt seems to show a lot of nouveau kernel messages, which might be the problem...
Could you please try installing the proprietary nvidia driver? I think the latest Nvidia driver supporting your GPU is version 340: sudo apt install nvidia-340 ** Summary changed: - Severe graphical corruption in gnome-shell + Severe graphical corruption in gnome-shell with nouveau [Nvidia GeForce 8400M GS] ** No longer affects: ubuntu ** Changed in: gnome-shell (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/1711936 Title: Severe graphical corruption in gnome-shell with nouveau [Nvidia GeForce 8400M GS] To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1711936/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs