Download this manual: W500 repair manual and then disassemble your laptop. Remove all the dust from the inside. You will need a vacuum cleaner and a brush. You might also need some small screw drivers. If the fan is completely broken the laptop won't boot at all because he will halt during the boot process with a fan error.
Some duct tape would be handy, too. You could fix it on the table and then put all the screws you loosen onto the tape. This way they won't get lost and you could more easily remember where each screw belongs to.
If you feel confident you could also disassemble the complete fan part and put some WD40 in the fan. But you will have to pull the fan out of his socket. This will surely remove any warranty left. I did it a few times with my laptops and they all run fine and without any noises. To get to the fan in one of my laptops I had to use a drill to get rid of some rivets.