World of Warcraft Mop Achivments are disabled?

Are you using any addons to disable it?
If not try rename your interface folder to something like interface2 and launch wow and see if they're still disabled. If not then it's an addon blocking it.
If it still doesn't work try renaming your WTF folder and launching wow and testing it. If that fixes it then there is something in your settings that is blocking it.
Hope this helps.