Reset Windows 7 to mirror display without a working monitor?

Question

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.

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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.)

Answer 1

I figured out the following workaround. I will mention first that I started up the computer normally with the DP cable already plugged in. I don't think this was a necessary part of the fix, but I mention it just in case.

Opening up the display properties, I clicked "detect." It added "Another display not detected." I then chose "Try to connect anyway on VGA" (which is not in use). This then gave me the option to choose "mirror these displays."

Then I got the Dell monitor to show in the properties (unused) without my laptop screen blanking out. Yay! And I changed the settings from "mirror on 1 and (nonexistent) 2" to "mirror on 1 and (Dell) 3." Which worked, and showed the low-res version on the 4K monitor as it originally had.

I got rid of the nonexistent monitor entry, and then changed to "extend these displays" and it is working perfectly again.

I did try the "show only on 2" one more time. It put both screens black and showed nothing, but fortunately the timer-based revert action worked correctly this time, so I didn't have to reboot again.

So for now I'm leaving it on "extend these displays" with my laptop monitor as a useless piece of screen real estate where I'm sure I will occasionally lose my cursor...but oh well, 4K is working beautifully and that's good enough. :)

If I find out how to get it working singly (without also having to run the built-in monitor) I'll update this post with how.