I clicked the tab of a sheet and then right clicked and chose 'Move or Copy'.
I checked the box of 'Create a copy' and clicked 'OK'. But nothing
happened.

The file has only 3 sheets total. Before, I accidently ran a macro to create
many sheets, but I deleted all of them with 3 sheets left.

I have never encountered such situation. This method has always worked
until today.

Thanks for help.