Lights work,nothing else does !

Dear Sir/Madam,the above mentioned fridge/freezer suddenly quit working.The lights in both compartments are on but nothing else works,l have replaced the thermostat,all to no avail.l am getting advice along the lines of…1st,replace the compressor relay,2nd,if that fails,replace the compressor,and,finally,if that also fails to solve the problem,then it’s probably the main board.l don’t really wish to replace any parts that are not necessarily faulty.So,what,in your opinion,is the most likely cause of the problem and what do l need to replace too solve this problem ? l’m not at all happy about having to consume warm beer !