I have a 27" iMac and I'm using Samsung SyncMaster SA850 as a second monitor (connected via a displayPort cable with a mini DisplayPort adapter).
Everything worked fine until yesterday - the Samsung screen turned black and now it only works with max resolution 1280 x 1024 (native is 2440x1440). I think I upgraded Lion 10.7.2 to 10.7.3 (I don't remember for sure though).
When I connect the monitor to an iMac with 10.7.2 everything works fine. And another iMac with 10.7.3 has the same problem as me.
Any ideas what could be wrong, please?