Cake problem .. please help!?

I love to bake cakes, and I put on fondant, and everything. But I have problems with making a cake. Whenever I bake a cake, I let it stay on the counter for a while like maybe a half an hour, and then I flip it upside-down and it all falls apart.. What do I do to keep it in one piece? And When I spread the icing on my cake, it all crumbles and there is cake chunks mixed in with the icing and stuff.. how do I make it all one cote of icing all around the cake?