How can you break up a five lb bag of sugar that must have got moist now is as hard rock?

Second, microwave the bag of sugar on high for 30 seconds at a time until it heats. This should help break up the clumps. (NOTE DO NOT OVERHEAT as sugar can melt quickly)

Alternative solution, take a hammer or any sturdy item and begin breaking the solid mass into fine chunks with the use of force. Repeat for all the parts inside to ensure that there are no whole solids present. Continue until small enough chunks.