onix45:
I have a project where i use logic level mosfet turn on or off 7 computer fans.
These fans are simple computer fans that work off of 12V.
Very strange. The mosfet you chose is just fine to use in that circuit. The Arduino can certainly drive the gate (in fact, the 100 ohm resistor in the gate circuit isn't needed - although that's not your problem).
I see no reason why you should be having this problem. Is your power supply staying at 12 volts at full load?