I had a stable 12.04 machine running perfectly.

The machine was booted without the monitor connected - since then the system always boots to low graphics mode. Onboard graphics (from lspci): VGA compatible controller: Intel Corporation 4 Series Chipset Integrated Graphics Controller (rev 03) Monitor: AOC e2450Swh

Display widget shows monitor as laptop(!?) and system details shows graphics as Gallium 0.4 on llvmpipe (LLVM 0x300)

X-server log appears to show correct monitor detected. When I boot from a live CD I get full 3d graphics

I've tried the monitor on a different machine - all OK. I've tried a different monitor on this machine - same problem.

Between having a working system and a broken one there have been no updates and I have made no configuration changes...

EDIT: I have come to the conclusion that the problem is caused by a known issue with lightDM hanging on battery check. I've managed to get 3D graphic working by switching to using GDM - not a solution but acceptable workaround. I would still like to know what is causing the problem and how I managed to get my system into this state!