Connecting fans in series or paralel?

Ok so i have found out that my arduino pin only gives 2.1V when high. That keeps the mosfet from fully opening i believe.

Why is that?

Its pin 36 on arduino mega 2560. I also have 7 servo motors attached to pins 22,24,26,28,30,32,34.

Could the servo library somehow change my pins output because of the ammount of servos conneced, or the particular pins i chose?