Looks to me like OctoPrint is running on a privileged port.
Did you change the port in the config.yaml?
If that's the case change it back to 5000 - if not try to start the server on a different port like 5001 with
I checked the config.yaml file, there was no reference to a port within the file.
Next I started Octoprint on a different port. I was able to run Octoprint and login.
I'm not sure why port 5000 would be a privileged port.
I was unable to get Octoprint to use the default port 5000 with any configuration. As suggested I hard coded a different port in the config.yaml file. Even after opening the ports in Windows security port 5000 was a no go.
But everything is now working.
May I ask to which port you changed it (in case someone else runs into the same issue) and ask you to try it again on port 5000 as administrator? (just press the windows key, enter cmd, right click on it and then on run as an administrator for a command line with admin privileges)
We're just curious if the port can't be used at all or just not by a normal user.