You can set time scale to 0, anything should stop moving until you set it back to 1. Still some will not be paused like mouse/touch inputs I believed.
Another way is to put the events that moves/updates those objects into a group and deactivate it when game over.
https://www.construct.net/en/forum/construct-2/how-do-i-18/stoppause-layout-completely-109728
Might be a good way to pause the game: https://www.construct.net/en/tutorials/advanced-game-pausing-400