My cat won't eat his food.?

We give him Whiskas Temptations also called"Kitty Crack" in our house. He always has Biscuits and we will normally give him Felix pouches and sheba as a treat, but he has started not eating these at all, he just sits by the cupboard where we keep the Temptations. This has gone on for 2 or 3 days now and Im starting to get really worried. What do I do?