My 18 month old Smeg fridge has stopped working ?

I turned it off two weeks ago when I went away and when I turned it on again two days ago - it would not get cold inside, but seemed to actually get slightly warm inside the fridge. The unit at the back got very hot so I turned it off again - have been trying it ever since but it won't go cold and is only making the smallest start up noise (usually you can hear it starting up) and stops after a minute - then the back gets hot and inside warm. Does anyone have any idea what could be happening? I wondered if the gas has leaked out unbeknown to me or is this not possible?