Please make sure there are no loose connections to the till & sockets, and that the socket has been turned on at the relevant plug at the wall and extension lead if relevant.
If you have other tills on site, Please test one of the power supply bricks from these tills on the till that is having issues. This may help narrow it down to either the lead/power supply or the till.
Ensure there is no damage to the till itself. This may be water damage and may be hard to see if it has dried up.
Is there a light that can be found either on the Power Supply brick or the till? If so and the till is not responding to clicks on the screen, please contact our support team with the info above on what has been tested and we will advise/replace accordingly.