NEED C WIRE HELP FOR NEST - NO POWER

I have spent several days searching the Internet, watching YouTube videos, and reading diagrams and hit a dead end. I’m trying to install a nest 3 and like many, I didn’t have a common wire. It was hidden in the wall so I connected it to both the thermostat and the furnace. In most cases, that’s the solution. In my case, I have no power going to it. I can really use some help. I wanted to add a picture but I’m not a regular Reddit user and can’t seem to find an option to add an image. Thank you very much in advance!