KDE doesn't start up: Could not connect to d-bus server

I haven’t restarted my workstation for a while because I’ve been busy running simulations for a while. This morning I thought it would be a good idea to update my system and restart it:

sudo zypper up
sudo reboot

I’m currently on kernel 4.3.31-30-default, KDE Plasma version no idea, but probably 5+. Is there a way to check without actually being in KDE itself? For example, asking for which version of kate I have installed reports with this:

QXcbConnection: Could not connect to display
Aborted

After restarting the system, I get this cryptic error message along with a blank screen:

can't start D-Bus. Can you call qdbus-qt5?

Rebooting into runlevel 3 gives me no problems (I’m pretty sure this is a desktop issue), so I was able to log in and call qdbus-qt5. This was my output:

Could not connect to D-bus server: org.freedesktop.DBus.Error.NotSupported: Unable to autolaunch a dbus-daemon without a $DISPLAY for X11

This looks like a related thread, but I think the issue there came down to repositories which I don’t have, which it less applicable. Running zypper lr -d comes up with the following:

#  | Alias                           | Name                                                       | Enabled | GPG Check | Refresh | Priority | Type   | URI                                                                                    | Service---+---------------------------------+------------------------------------------------------------+---------+-----------+---------+----------+--------+----------------------------------------------------------------------------------------+--------
 1 | devel_languages_python          | Python Modules (openSUSE_Leap_42.1)                        | Yes     | (r ) Yes  | No      |   98     | rpm-md | http://download.opensuse.org/repositories/devel:/languages:/python/openSUSE_Leap_42.1/ |        
 2 | download.nvidia.com-leap        | nVidia Graphics Drivers                                    | Yes     | (r ) Yes  | Yes     |   99     | rpm-md | http://download.nvidia.com/opensuse/leap/42.1                                          |        
 3 | download.opensuse.org-non-oss   | Main Repository (NON-OSS)                                  | Yes     | (r ) Yes  | Yes     |   99     | yast2  | http://download.opensuse.org/distribution/leap/42.1/repo/non-oss/                      |        
 4 | download.opensuse.org-non-oss_1 | Update Repository (Non-Oss)                                | Yes     | (r ) Yes  | Yes     |   99     | rpm-md | http://download.opensuse.org/update/leap/42.1/non-oss/                                 |        
 5 | download.opensuse.org-oss       | Main Repository (OSS)                                      | Yes     | (r ) Yes  | Yes     |   99     | yast2  | http://download.opensuse.org/distribution/leap/42.1/repo/oss/                          |        
 6 | download.opensuse.org-oss_1     | Main Update Repository                                     | Yes     | (r ) Yes  | Yes     |   99     | rpm-md | http://download.opensuse.org/update/leap/42.1/oss                                      |        
 7 | ftp.gwdg.de-suse                | Packman Repository                                         | Yes     | (r ) Yes  | Yes     |   99     | rpm-md | http://ftp.gwdg.de/pub/linux/packman/suse/openSUSE_Leap_42.1/                          |        
 8 | repo-debug                      | openSUSE-Leap-42.1-Debug                                   | No      | ----      | Yes     |   99     | NONE   | http://download.opensuse.org/debug/distribution/leap/42.1/repo/oss/                    |        
 9 | repo-debug-non-oss              | openSUSE-Leap-42.1-Debug-Non-Oss                           | No      | ----      | Yes     |   99     | NONE   | http://download.opensuse.org/debug/distribution/leap/42.1/repo/non-oss/                |        
10 | repo-debug-update               | openSUSE-Leap-42.1-Update-Debug                            | No      | ----      | Yes     |   99     | NONE   | http://download.opensuse.org/debug/update/leap/42.1/oss                                |        
11 | repo-debug-update-non-oss       | openSUSE-Leap-42.1-Update-Debug-Non-Oss                    | No      | ----      | Yes     |   99     | NONE   | http://download.opensuse.org/debug/update/leap/42.1/non-oss/                           |        
12 | repo-source                     | openSUSE-Leap-42.1-Source                                  | No      | ----      | Yes     |   99     | NONE   | http://download.opensuse.org/source/distribution/leap/42.1/repo/oss/                   |        
13 | repo-update                     | openSUSE-Leap-42.1-Update                                  | Yes     | (r ) Yes  | Yes     |   99     | rpm-md | http://download.opensuse.org/update/leap/42.1/oss/                                     |        
14 | science                         | Software for Scientists and Engineers (openSUSE_Leap_42.1) | Yes     | (r ) Yes  | No      |   98     | rpm-md | http://download.opensuse.org/repositories/science/openSUSE_Leap_42.1/                  |        

On this bug report page from ubuntu, they recommend you change around some sources (specifically /usr/bin/startkde) to fix the issue, but I don’t understand what that does and I’m worried I could create an irreversible change.

I have qdbus-qt5, but I don’t know how to solve this error. I would appreciate any help I could get.

Cheers,
C

After booting to (old syntax) Runlevel 3, please post the systemd journal entries for the “–this-boot” following an “init 5”.
At Runlevel 3, you could also post the systemd journal entries related to the D-Bus.
Are you sure that you have a 4.3 Kernel?On my Leap 42.1 system the Kernel is 4.1.31-30-default.

This is not a dbus issue. The output says there’s no display provided by the X server. Whenever NVIDIA is involved this usually means there’s something wrong with the driver/kernel module, which should be provided by the nvidia repo.
What you should be able to do, is to boot the previous kernel, through the Advanced options in the GRUB2 boot menu.