Hotpoint Mistral Plus Frost Free?

I recently purchased this fridge/freezer second hand (about a month ago) and it worked perfectly. Now though, the fridge is not cold and the fan only works intermittently. Looking back at other problems with this appliance on the web I followed one suggestion by removing the intake air cover below the freezer and removing the fluff. It still isn't working properly. Before I call the Hotpoint engineer in and pay an extortionate amount to repair I was wondering if anyone may be able to offer some assistance. Many thanks.