I have a Windows 7 laptop (specifically, an hp ProBook 6470b) and a brand new Dell U2718Q UltraSharp 4K monitor.
When I hooked up the monitor (using a DisplayPort cable - DP to DP, no mini-DP), it worked fine showing the low resolution of the laptop screen. The display settings of Windows 7 were set to "mirror display."
I installed the driver using the disk that came with the monitor. So far so good.
I set the display settings to "extend these displays." It still worked perfectly.
Then I chose the fatal "show display only on 2" option. It worked—for about a second. I DID NOT click the "keep these changes" button. Then the screen started flickering, showing two full desktops side by side (the same one twice, each taking half the screen), with some crazy colored noise across the top. The laptop monitor was off for this. And then the 4K went fully black also.
When it went fully black the "will revert changes in __ seconds" had shown 7 seconds. So I waited. But the changes never reverted. I unplugged the DP cable and the laptop stayed black. I shut the lid (which usually puts the computer to sleep even when I don't want it to) and the laptop went on running. I finally had to hold the power button down to turn it off.
After restarting, I haven't been able to get ANY picture on the 4K monitor for more than a couple seconds (with flickering). Because I can't revert the multi-monitor settings to "extend these displays" (which was working perfectly), because that option does not appear in the display settings control pane when the external monitor isn't plugged in. And when the external monitor is plugged in, I can't see anything at all to choose the settings I want.
How can I set the multi-monitor preferences on a Windows 7 laptop with no external monitor plugged in?
(Or better yet, how can I make this 4K monitor just magically work as a single monitor with my laptop. But I think the first question is more answerable.)