I have windows 10 64 bit and Radeon HD 4850 card. I found out that my system recently updated drivers into version 15.200.1062.1003 from 28.07.2015 via Windows Update.
Sorry for polish on the screens, but I hope that doesn't have too much impact.
Couple of thing happened then:
I therefore manually reverted the driver to previous one: 8.970.100.9001 from 13.01.2015, which is working properly: it recognizes two connected displays, and allows to choose proper resolutions: 1920x1080 and 1280x1024.
However with this driver some of videos (mostly through Silverlight VOD components) don't play correctly - I can see only green screen. I was curious and checked and it looks like new driver solves that issue for me. However due to the other factors I had to revert anyway.
I would appreciate any guidance how to solve the issue.
Here are my specs, FYI: