Was dust just holding the fan from spinning?
Can you freely spin the fan now with little effort - can you visual see the fan is not spinning or attempting to spin?
I believe you can buy a additional cooler that will fit on this card if its borked
http://www.overclockers.co.uk/showproduct.php?prodid=HS-047-AK
Something like this - you will have to check your card is okay with this - but you get my meaning for a cheap fix