Full factory reset??
Factory reset universal
Power off the TC.. ie pull the power cord or power off at the wall.. wait 10sec.. hold in the reset button.. be gentle.. power on again still holding in reset.. and keep holding it in for another 10sec. You may need some help as it is hard to both hold in reset and apply power. It will show success by rapidly blinking the front led. Release the reset.. and wait a couple of min for the TC to reset and come back with factory settings. If the front LED doesn’t blink rapidly you missed it and simply try again. The reset is fairly fragile in these.. press it so you feel it just click and no more.. I have seen people bend the lever or even break it. I use a toothpick as tool.
N.B. None of your files on the hard disk of the TC are deleted.. this simply clears out the router settings of the TC.
Since you are doing this from windows.. it is absolutely no surprise that it is not working.
You did not factory reset if the led is green.. after a factory reset it will flash slowly amber. Please do the factory reset again..
After you do that use ethernet from the computer and ensure your computer is getting an IP 10.0.1.2 (maybe something else but normally 2).. and the gateway should show 10.0.1.1
Open a command window and ping the extreme..
If it fails to respond windows has automagically decided to move location to public or work. Force it back to home.
OR
It has slammed up the firewall.. turn off the firewall.. the airport must respond to pings.
When you complete the setup via the ethernet then disconnect and see if the wireless is the problem.
If you need to .. remove the AE from the network and plug it directly into the computer with ethernet patch cable. You can do this setup in full network isolation.