Abit NB fans are notorious for failing early and often. Getting rid of that fan (or any other small fan on the NB that requires high speed to move any air) was one of the four best things I did to reduce my PC's noise.
A passive NB heatsink works fine on these boards if you've got some airflow from the CPU HSF like a Zalman CNPS 7000 or Thermalright XP/SI-120. They won't work as well with a tower-type CPU HSF.
Some have had success by just removing the fan from the stock NB HS. I'm using a
Zalman NB47J, attached to the wire loops with
a bicycle spoke bent to fit - its been working great for almost two years. Unfortunately, the wire assembly from the stock NB HSF is not adaptable to aftermarket heatsinks.
There are are several high performance passive coolers that now include the wire loop mounting provisions -
Zalman NBF47 and
Thermalright HR-05. Be sure to clean off the original "bubble gum" thermal pad and use the thermal grease included with the new heatsink or Arctic Silver Ceramique (good when there are exposed components nearby).