the fan has stopped working?

You need to open the case.
Disconnect the charger and remove the battery.
Open the case.
Locate the CPU fan.
Check that it's properly connected.
If the fan IS properly connected but don't work, remove it. It can be a good idea to take a photo of the actual fan before you remove it to help you remember exactly how it's mounted.
Go to a computer shop with the old fan and ask for a similar one. It don't need to be identical, only of the same general shape, have identical mounting requirment, and been no thicker than the old one.
(a thicker fan may not allow you to close the case AND can severly restrict the air flow)
Install the new fan and connect it.
Close the case.

Electro
July 2012