If you go to the Visual Basic editor (by pressing Alt and F11) and insert a module by going to the Insert menu and clicking module. Now in the white space on the right type the following:
Code:
Sub turnOffMenuBar()
Application.CommandBars("Worksheet menu bar").Enabled = False
End Sub
Sub turnOnMenuBar()
Application.CommandBars("Worksheet menu bar").Enabled = True
End Sub
Now close the visual Basic editor so you are back to your worksheet and the easiest way to run these is to go to Tools menu, Macro, Macros (or press Alt and F8) and then run whichever of the two functions you need.
If you need this to automatically do this every time it opens then there's a little more to it.
Also if you wanto disable any command bars just copy and paste the
Application.CommandBars("Worksheet menu bar").Enabled = True
line and insert just after this (before the end sub) and then change the "Worksheet menu bar" to whichever toolbar you need - e.g. "Standard"