when attaching 2nd monitor, both screens change to right50% of desktop

I have a Dell laptop (running Windows 10), a Targus docking station, an old LG monitor that I'm trying to replace, and a new AOC monitor that I want to use instead. I am trying to attach the AOC monitor directly to the HDMI port on the laptop, since the monitor screen doesn't display as smoothly when it's connected to the docking station. The trouble is that when (and only when) the laptop is attached to the docking station, if I then plug the AOC monitor into the HDMI port on the laptop, both the laptop screen and the AOC screen switch over to showing the rightmost 50% of a Windows desktop:



This isn't usable, because when I open new apps, even though I can see their icon on the taskbar, the app has opened in the left-hand 50% of the desktop, which is not displayed on either screen. I know there is a "hidden half" of the desktop off to the left, because I can move the mouse pointer off of the left border of the screen(s), and then I have to drag the mouse pointer back by an equal amount before it becomes visible again.

Now, when the laptop is not connected to the docking station, everything works as expected. I can connect either the LG monitor or the AOC monitor directly to the laptop, and I can go into Display settings and choose to duplicate the screens, or extend the desktop across both screens, and all options work as they're supposed to. Here is the desktop duplicated across the laptop screen and the LG monitor:




and here it is duplicated across the laptop screen and the AOC monitor:


But, as soon as I connect the Targus docking station, the laptop only works correctly with the LG monitor. Here it is with the LG monitor connected, and the desktop nicely duplicated between the laptop screen and the LG screen:


However, as soon as I connect the AOC monitor instead, I get both screens showing the right-50% of the desktop, as shown in the very first picture.

How do I prevent that?

I do know that the laptop seems to count the Targus docking station as a "screen" (presumably because the Targus has a DVI connector on it). When nothing is connected to the laptop, Display settings shows 1 screen. When the Targus is connected, Display settings shows screens "1" and "2". And then when the LG monitor is connected, the laptop screen and the LG monitor become 1 and 2, while the Targus gets bumped down to 3. But, regardless, that still doesn't explain why the laptop is showing the rightmost-50% as soon as the AOC gets connected to it, and why this doesn't happen with the LG monitor.

The only other difference is that the LG monitor (the one that works) has a DVI connector which is then connected via a DVI-to-HDMI converter to the HDMI port on the laptop, whereas the AOC monitor (the one that's acting screwy) is connected via an HDMI connector straight to the laptop. Don't know if that affects anything.

Thanks, this did help fix it! When I connected the new monitor and got both screens showing the rightmost 50% of the desktop, I just hit windows-P and the menu appeared (since it appears by default on the right-hand side of the screen, that meant of course it was part of the 50% of the desktop that I could see). And from there I could edit display settings and get it fixed.