Hi, since your name is Settebello I assume that you might be Italian or, at least, know a thing or two about Italian trains.
The lever with positions 0 to 6 is NOT like the potentiometer installed on locos like E444 / E444R or E656 / E656N, rather it's the field shunt that you use to increase the speed when you already have all resistors excluded.
EU07* and ET41 have manual controls, like the E646 - but with more complex circuits, so there are a few differences in the behaviour and it's not as straightforward as on a E626.
After the loco is turned on (you definitely hear it), in order to move the train you need reverser in forward position,
field shunt to zero, loco brake to zero, continuous brake to normal (the 3rd position, which makes the pressure in the main pipe go to 0.5 MPa or 5 bar); then throttle in 1st position, wait until you have current in the motors, then you can increase the throttle as you like.
After you're over all the series position, you hear the resistor fans turn off; you are now able to increase the field shunt from 0 to 6, gradually; eventually you can set the field back to 0, give another notch on the power wheel and you are now in parallel. Increase the throttle until you're at end parallel, again the resistor fans switch off and you can again use the field shunt from 0 to 6.
Failure in releasing the brakes on the whole train will not stop you from departing, since the brake pressure relay only looks at the pressure in the brake cylinders of your loco.
Forgetting to depart with the field shunt set to 0 will not stop you at first, but will cause problems later on (now I don't remember what happens, to be honest).
Not spending enough time in position 1 on the throttle won't allow you to give current to the motors.
I hope this will help, anyway we're here
* p.s. all the similar locos are included, so EU06, EU07, EP07, EP08.