First, if you're looking at a chart sheet (not a worksheet), you shouldn't see
the Worksheet Menu Bar.

I'd try this first.
Activate a worksheet.
Then rightclick on an empty spot on any toolbar.
Customize|Toolbars tab|
Select worksheet menu bar and click Reset.

Then check to see if it worked.

If it didn't, I'd do this next:

Hit alt-f11 to get to the VBE (where macros live)
hit ctrl-g  to see the immediate window.

Type this and hit enter:
application.commandbars("worksheet menu bar").enabled = true

Back to excel to see if it worked.

If that didn't work, maybe you can just delete the file that excel uses to keep
track of toolbars.

Close excel
Windows search button
search for *.xlb
(in hidden folders, too!)

Rename all you find to *.xlbOLD
(or delete them???)

This will remove any customizations that you've made to any toolbar.  You'll
have to rebuild those at your leisure.

If you're happy with the results, delete the *.xlbOLD files.

If you're not happy, close excel and rename those *.xlbOLD files back to *.xlb.