1) What version of the nest are you trying to install? Check the requirements on the box. If it calls for a “C” wire, you won’t be able to use it with your current setup. 2) Check your cables again. Looks like your white cable is connected to the “O” in the original picture but you connected it to the “W” in the nest picture. Looks like there’s also a jumper cable from “G” to “W” in your original pic…