Need help wiring new dimmer
Your problem is that the white wire that is connected to the new dimmer never actually connects to neutral -- it simply connects to the load.  You'll need a white pigtail and a new wirenut to fix this.

Turn the power off at the breaker. Undo the existing wirenut for the white wires, and undo the white wire from the new dimmer.  Twist one end of the white pigtail and the white wire that was undone from the new dimmer with the existing bundle of white wires, and put the new wirenut on.  Attach the other end of the pigtail to the new dimmer and put everything back together, then turn the power back on and enjoy your new dimmer!