Hi,
Here is a link to the [ftp://ftp.dell.com/manuals/all-products/esuprt_laptop/esuprt_latitude_laptop/latitude-e4200_service%20manual_en-us.pdf|service manual] for your laptop.
Click on the ''Fan'' link in the Contents page (opening page) to view the necessary pre-requisites and then the procedure to remove and replace the fan.
Replacement fans are available from various sources. Just search online for ''Dell Latitude E4200 fan'' to get results for suppliers and choose the one that suits you best.
Hopefully this is of some help