Ok I have an Acer Aspire 1820PT


I was using it about a month ago, when a godawful crunching sound happened inside it, I shut it down, and have booted it up only once since, it seemed to work fine however I can't hear a fan working, which previously I could. so my questions is,

How hard is it to replace the fan in an acer, i have dismantled and reassembled an elderly compaq to clear a noisy fan, but the acers look a bit more technical.