You can login to your router admin panel by entering the numbers 10.0.0.1 in the address bar of any web browser. (the same place you enter web addresses). This should open up an Xfinity admin panel. (admin = admin and password = password). These are default login credentials if nobody has changed them.
Update: Since my Roku stick is a few years old, I went to Walmart this afternoon and purchased a new Roku Streaming Stick 4k+. I brought it home and tried to set it up and received the same issues as my old one: it was unable to connect to the internet. Glad I saved the receipt!
From the image you sent after initially entering 10.0.0.1 that indicated you needed to complete activation, I think it may have been a combination of the power outage corrupting settings and the Xfinity/Comcast rep you spoke to this AM resetting your network.
By changing your wireless network name and password, basically just refreshed the entire network and gave you a fresh start if the Roku device was having a problem authenticating either the name or password.
Good thing is you now know how to access your router and look for problems.
Now go stream some movies.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102