Did you press the special function key to turn on the external display port or clycle thru the availabel option? Its usually Internal, Internal+External, External, and then back to the beginning. Its a key combo like Fn+F4
Yes. That same selection is available under the Screen Resolution control, and when I select "Extend" or any other option, it says "Unable to save display settings" as though it doesn't know how to handle the display at all.
When I try to run Catalyst Control Center, I get a dialog "Catalyst Control Center has stopped working, looking for a solution ..." which never succeeds.
Is there an ".inf" file for that monitor? Its the 39 inch 4K monitor by Seiki, which displays OK at 30 Hz on my Nvidia card under Linux.