Perhaps there is an installer image for Beowulf somewhere and this can
be solved with a fresh re-installation? Sunday, I did an in-place
upgrade from Ascii to Beowulf on amd64. I have only partial graphics
since and must get past some problems with (I think) X11.

When I allow slim, lightdm, or xdm one at a time (removing the others)
to start, the keyboard and mouse do not respond not even to switch to
a console even though they cause the display to show the graphical
login screen. However, when I disable / remove these display managers
then startx gives some lip about modules not existing.

When I run startx manually from a console, something similar happens
though I get a blank graphical display with the unmovable mouse
pointer centered on the screen. But the window manager seems not to
be running nor the desktop environment and, again, both the keyboard
and the mouse are unresponsive so timeout is a way to get it to drop
back to the shell.

$ timeout 15 startx

X.Org X Server 1.20.0
X Protocol Version 11, Revision 0
Build Operating System: Linux 4.9.0-6-amd64 x86_64 Debian
Current Operating System: Linux slimbook 4.17.0-1-amd64 #1 SMP Debian
4.17.8-1 (2018-07-20) x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.17.0-1-amd64
root=UUID=3f66d242-f064-4f6e-a110-6974886fb9a4 ro quiet
Build Date: 01 July 2018  05:07:24PM
xorg-server 2:1.20.0-3 (https://www.debian.org/support)
Current version of pixman: 0.34.0
        Before reporting problems, check http://wiki.x.org
        to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
        (++) from command line, (!!) notice, (II) informational,
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/home/lars/.local/share/xorg/Xorg.0.log", Time: Tue
Aug 21 14:36:43 2018
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
xf86EnableIOPorts: failed to set IOPL for I/O (Operation not permitted)
(II) modeset(0): Initializing kms color map for depth 24, 8 bpc.

$ grep '(EE)' ~/.local/share/xorg/Xorg.0.log
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[ 22631.982] (EE) Failed to load module "nv" (module does not exist, 0)
[ 22631.984] (EE) Failed to load module "fbdev" (module does not exist, 0)
[ 22631.985] (EE) Failed to load module "vesa" (module does not exist, 0)
[ 22631.989] (EE) [drm] Failed to open DRM device for (null): -2
[ 22632.296] (EE) Failed to initialize GLX extension (Compatible
NVIDIA X driver not found)

$ lspci -nn | grep -E -i 'vga|3d'
00:02.0 VGA compatible controller [0300]: Intel Corporation Device
[8086:5916] (rev 02)
01:00.0 3D controller [0302]: NVIDIA Corporation GM108M [GeForce
940MX] [10de:134d] (rev a2)

$ sudo lshw -sanitize -class display
  *-display
       description: VGA compatible controller
       product: Intel Corporation
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 02
       width: 64 bits
       clock: 33MHz
       capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:128 memory:dd000000-ddffffff
memory:b0000000-bfffffff ioport:f000(size=64) memory:c0000-dffff
  *-display
       description: 3D controller
       product: GM108M [GeForce 940MX]
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:01:00.0
       version: a2
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list rom
       configuration: driver=nvidia latency=0
       resources: irq:16 memory:de000000-deffffff
memory:c0000000-cfffffff memory:d0000000-d1ffffff
ioport:e000(size=128) memory:df000000-df07ffff