Just says 'fill water'

Question

HiI have just been given a Nespresso Magimix M300 (also called D300 I think) by a friend and it was working fine at her house. Now I've cleaned it all up, put water in the tank but when I turn it on it keeps saying 'fill water'. Obviously it thinks the water tank is empty and the water is not going to wherever it is meant to go. Does anyone have any ideas please?