when nothing else works- try Safe Mode.
It really is the solution. Inhibits all at normal.
Bypassed all the BS- 'Access Denied' and 'This app is being used' etc. Alter the host File in Safe mode... and you don't need notepad in admin mode, etc..
IF you keep logging in safe mode look for msconfig under System 32... just accessing the application Is enough to bump you out of it.
All will be good after@!