unable to boot into graphical mode after kernel update

openSUSE 13.1 After a patch update today I am unable to boot into graphical mode.

The system is an HP N45L used intermittently as a backup archive machine. The graphics device is an on-board ATI Radeon with AMD RS785E chipset. No graphics drivers are installed - so native resolution only, using “drm_kms_helper.edid_firmware=edid/1024x768.bin” in the boot line after previous advice from this forum. The system has been dormant for 2 months, so 10 or more patches were installed today, including a new kernel, identified in the GRUB2 boot line as: vmlinuz-

On re-booting, there was an extended delay (2-3 minutes) before the system showed the normal Plymouth boot screen. Then the boot process proceeded but stalled at ‘Reached target Graphical Interface’. A few entries above that, the boot screen shows: [DEPEND] Dependency failed for LSB: X Display Manager. I get similar results booting the current and previous kernel versions, even with “failsafe”.

The system boots into terminal mode (3) with errors, most of which roll off the screen before I can read them. These two remain visible:
] ERST: Failed to get Error Log Address Range.
] i8042: No Controller found.

On ‘startx’ the following errors are reported:
auth: file [user] .serverauth.1957 does not exist
(EE) Fatal server error:
(EE) Cannot move old log file “/var/log/Xorg.0.log” to “/var/log/Xorg.0.log.old”
xinit: Unable to connect to X server: Connection refused
xinit failed. /usr/bin/Xorg is not setuid, maybe that’s the reason?

I would be grateful for technical advice to help diagnose and resolve this issue. Thank-you.

Tried su - root ‘startx’ - GUI comes up as normal.
Perhaps standard Xorg file permissions are corrupted?
Which files are relevant and what are their correct permission and SUID settings?
Advice on X-org-wiki here is helpful but does not seem pertinent for openSUSE 13.1?
Grateful for pertinent advice from technically qualified openSUSE users.