Check all your lights to make sure they are working. It helps to have someone outside since they can check the brake lights for you as well. It's unlikely that the X3 throws a false burnt-out bulb light.

As for your tyres, check the pressures when cold and verify they are all correct. Visually check for any punctures as well. If all is well, push the reinitialise button (!) in the centre console and drive off.