If your cakes baked up flat, it may be that your raising agents are no longer active, so be sure to use fresh baking soda and fresh baking powder. It may also happen if you let the batter sit out for too long before baking. In this case the leavening agents will react in the batter and release gases before the batter sets and the gas will escape through the surface of the batter instead of being trapped as air bubbles in the cake crumb structure.