When I press the start button, there is a blank square window on top

My mom's Intel NUC5i5RYH is on Windows 10 single user has this weird problem. When you click/press the start button, you get this blank window ontop with loading animation.


When I click anywhere else, the box disappears. It only is there when the windows button is pressed. Any idea how to remove this box, since I can't see the rest of the start up menu.

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First of all, the quickest test is to restart the computer, and see if the issue persists. By "restart", I mean clicking "Restart" - not "Shut Down" (Shut Down saves the kernel ready for a fast boot next time). For my own troubleshooting, I do TWO Restarts - not just one.

Please give the step-by-step actions which start with a black screen and finish with the config shown in your photo.

A "step" is a user action, such as:

- Press this
- Click that
- Type something

Reason for my request:

- I can't see how any user can "click/press" a Start button. "Click" implies the use of a mouse. "Press" implies keyboard action - such as for a Start button, or maybe the touchpad.

- Normally, a single action can't start with a black screen and arrive at your photo. I can see icons at the foot of the screen, so does that imply that there's no "login" (no password)?

Is there an icon on the taskbar that corresponds to the white window? If yes:
- Is it active?
- Is it still active after the window disappears. If it is, you can drag the hidden window back on to the screen. The old way was to R-click on the icon, then click Move. But there's no Move option now. Anyway, if the icon is still visible and active, come back here and we can hack something.

Based on the suggestion by @Megahertz, you could try disabling Classic Shell and Taskbar Tweaker - if you use them.

In the config shown in the photo, does pressing Ctrl+Alt+Del cause the white window to close?

It probably will. But if not, you can see the process for the white window in Task Manager. Tell us what the process is.

You can try disabling all extensions. Then re-enable one a time to find the culprit - if any.

If all else fails, you can try Event Viewer to cover the previous shutdown and the current start (which shows the white window). But you will need to come back here for instructions on using "eventvwr.msc"

Thanks
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I've restarted the PC, and the problem is gone. I have no idea what happened. I just performed a windows update. All seems good for now. Will report if the problem persists.