Who can help me? i am playing warlord batllecry III and i have a question.?

ok so its like this. i have all the 4 parts from the set of thyatis and that should give me 100 magic resistance.the thing is when i look at my hero's information, my magic resistance is 0.do i have to activate somehow the set? can you tell me what do i have to do in order for the set to work ?