My MS Excel context menus have been disabled somehow?

hey yers.

some how (i dont know how) the context menus (right click ones) have been disabled when i rightclick the tabs to change sheets (should bring up insert / rename / copy etc function menu) and when i right click a cell in general.

now, this is not to do with a specific workbook, it is happening with any workbook i open on my own machine. Now, im guessing uninstalling and reinstalling will fix my problem -> but its a little long winded to do eh.

anyone know what could be causing it plz? (and more specifically, how i can fix it?)

tnx guys.
Wayne