Taskbar and Menu Properties - Customize does not work

[japp]

When I click on Customize nothing happens. To close it I need to use Task Manager. It has happened that a window has started blank and doesn't respond. Also this one I need to use Task Manager to close.

The PC also becomes unresponsive for a while. Also have needed to restart Explorer.

How can I solve this?

[HappyAndyK]

Using a 3rd party theme?

Try running sfc /scannow and see if it helps, else try a system restore to a prior point.