Has she turned down the volume yet?
No, she hasn't
....(not turn on the volume)...
I haven't turned on the volume yet
????
I've just turned up the volume
....not....
I haven't turned on the computer yet
...not...
I haven't logged in to the website yet
????
I've just turned off the computer
Has she turned on the computer yet?
No, she hasn't
Has he turned off the computer yet?
Yes, he has
???????
I've logged out of the website