Our computer at work was taken over by a virus that created a new user account. We couldn't get rid of using virus scanners. Locked us out of everything.
Got it back by.clicking ...my computer..Local disc...Security.
And discovered there was a new user with a Russian name.
I highlighted then denied all permissions on that user.
We regained control and was then able to run a virus scan which found and removed it.
Might be similiar situation?