T420s - loss of WDM / Aero on external monitor

[buzzlight]

Folks,

Wondering if anyone else has had this problem. I've used an external monitor for months without issues (T420s w/docking station using DisplayPort or DVI). Suddenly the Windows Desktop Manager and Aero have stopped working when docked and on the external monitor. I've tried to run the Aero troubleshooter but it can't find the problem. I suspect an update has caused this, most likely a graphics driver - so I also rolled back a graphics driver (NVIDIA NVS 4200M) to no avail.

When not using an external monitor, Aero works just fine on the native laptop display. When undocking, WDM needs to be re-started for it to work. When starting up with just the laptop display, it works fine.

Aside from this my system is clean, virus-free and exhibits no other problems. Anyone else had this issue and been able to solve it?

[buzzlight]

Hi folks,

I'm answering my own question. Turns out the culprit was a MS Windows update (platform update KB2670838). Since this is a recommended and not critical update, I uninstalled it - and Aero started working immediately on my external monitor. Full details here: http://answers.microsoft.com/en-us/wind ... 7ce8dd8480