The computer didn't restart. I pressed the restart button. (when-clause first)
When I pressed the restart button, the computer didn't restart.
The computer didn't restart. I pressed the restart button. (when-clause last)
The computer didn't restart when I pressed the restart button.
We have the battery for the camera. We'll call you. (when-clause first)
When we have the battery for the camera, we'll call you.