The 2N7000 mosfet in he video (datasheet) might not be enough for your fan.
Your fan is 400mA max, which presumably is the stall current, so only for brief periods like at start up. That's within the mosfet's maximum allowable "pulsed" current of 500mA, but might be a bit close especially if your fan actually does stall for any time longer than a "pulse", whatever that might be.
Then the fan specs don't say what the no-load current is; the mosfet continuous current is 200mA, but there's no way to say right now if that's enough.
If I were you I'd measure the current your fan draws when it's running and see if it's below 200mA. Remember that to measure current your meter goes in series with the load (ie, break the circuit and put the meter in the gap) as shown here; use a meter scale that will accommodate the 400mA maximum.
