I have two Magimix machines - neither the 3000 model - the smaller 3100 Compact and the tiny Micro - but the basic interlock principle is the same on all of them.
To run the motor requires two things - the mixing bowl to be fitted and the lid to be on - this is to preserve your fingers.
There's a spring loaded bar in the handle - the lid presses down on it when it's fitted correctly. The lid presses on the bar and the bar presses on the button you speak of.
My guess is that the lid is broken and not pressing on the bar and consequently the safety interlock is not being overcome.
There's a place in the UK that sells Magimix spares...
BBS - 01252 727755
Good Luck...
February 2016