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