If you're clock is not running it might either be due to the timer configuration or that you have forgotten to use the blue start button in the top right corner of Live Score. 

For a correct configuration see your Game Data andmake sure the setting makes sense.
So maybe an increasing timer that starts at second 0:00.

A decreasing timer that starts at 0:00, would not do anything, because it would count down from 0:00.

Afterwards please submit your changed game data setup, and maybe also reset your game to start with the new and fresh settings.

If you now press the blue start button, and then simply start the game and the clock with the controls, it should all work as expected.