Experienced this day, the joy of trying to reinstall everything on one computer in one room and searching for downloads on another in the next room. Both BB, both Aol, but different accounts.
One would be going nicely when I forgot and switched on the other.
In short it was necessary to pull the telephone connection from one while tinkering with the second computer if both had to be on at the same time.
At its simplest, without other controls, a second computer coming alive will stop access to the net for both.