Serial number not valid after reset

I finally got past the page requesting the serial number after trying many different things. I don’t know exactly which one worked but I’ll tell what I did. The problem I described repeated many times (at least ten) before I posted it and I did everything correctly so none of that was the issue. The error message just kept repeating. I tried an ethernet cable as someone suggested, seemingly to no avail, but I left it hooked up as my connection while I continued working the problem. I tried using "www.routerlogin.net" and "192.168.1.1" and "www.routerlogin.com" with no luck. Finally, frustrated, I typed "http://www.routerlogin.com" and got the same serial number request as always but this time it was accepted with no error message and continued to the setup menu. I was then able to change the SSID/password and other settings as normal. I have no idea if it was the ethernet cable access or the fact that I just kept trying or that I typed the entire "http://www.routerlogin.com" or some combination of all of it. Or maybe a stubborn electron got tired of resisting me. I had attempted logon with all the various addresses probably thirty times before I used the entire "http://www.routerlogin.com" address but the success (acceptance of the serial number) came the first time I tried that particular web address. I've since logged in using all of the above addresses multiple times with no problem and no more requests for the serial number. It now seems to work as it always had before. Maybe simple persistence won out. Yes, I am joking about that and the tired electron. I appreciate the reply trying to help but I seriously have no idea what finally worked or why. Maybe my story will help someone else. Maybe not. But there it is.