Im stuck on that too. Something I found to work is you have to put some Sapphire on the bottom part. only about half way. Then use Obsidian and pour some in the way of the laser thats shooting right. This clears the blockage. Keep on until the water flows. Once the water flows sprinkle more Sapphire over the tiny hole. The goal is to get the water to freeze so this helps it more. When the water freezes, it powers the second laser. Next drop some Citrine (yellow gem) in the way and it powers the larger light that shines on the zombie. This is where I have a problem. I have killed the zombie with Sapphires and Obsidian before but the stage wasn't cleared. Experiment around a bit.