Sounds like you might have corrupted your installation of Maya to be honest if it can't import the standalone module, but there's a lot more information I'd need to know before actually believing it. If you open maya, go to the script editor, open a python tab and then type:
import maya
import maya.cmds as mc
import maya.standalone as ms
and then run that, does it give you the same error or more errors? Did you do something to your environment variables? Are you running this at a studio with a very custom environment or from home?