what's wrong with my freezer fan?

I have a Hotpoint frost-free freezer (model FZA54T if that's important) that has stopped working properly. All the condensator gubbins etc seems OK, lights go on and off as expected, but the fan that is supposed to push the cold air around the unit doesn't. It fires up with the condenser etc, turns properly for about 5 seconds, then cuts out. Could I solve this problem by just getting a new fan motor from Hotpoint and fitting it myself (about £70 parts cost) or is it more complicated than that?