Connected, No Internet - WiFi Range Extender WN3000RP

Fixed!

1. I did a factory reset

2. Instead of Option 1 in the manual (Connecting with WPS), I did Option 2 (Connecting with web browser setup guide) detailed below:

2a. following the steps, I first connected to NETGEAR_EXT in my network manager.

2b. I opened a web browser on the same PC but the onscreen setup guide did not automatically appear. So I found my range extender's IP address, which I did by connecting to my router and looking at the connected/attached devices (device name = WN3000RP).

2c. I then typed the IP address into the browser on my PC, the onscreen setup guide appeared

2d. I entered the username and password

2e. I selected my router from the options available and entered the password/passphrase for the router.

2f. I changed the suffix of my range extender to _EXTENDER instead of _EXT (I don't know if this is important but I thought it was best to have a completely new name so that my other devices would have a new WiFi Network to connect to, and prompt me to enter a new password)

3. I connected my PC to the renamed range extender.

4. I connected my other devices to the renamed range extender.

They all work! No more "Obtaining IP address" or "Connected, no internet"!

Maybe it's important to note that before doing any of the above, I had previously updated the firmware on the range extender. The factory reset did not undo this change, the firmware remained up-to-date. 

To update the firmware was relatively simple: again it was a question of connecting to the range extender via a browser and I did this by getting the IP address from the list of connected/attached devices on my router. The URL given in the NetGear documentation (www[dot]mywifiext[dot]net) did not work.

Why this method worked when the previous WPS button connection method had not, I have not idea! But thankfully now I don't have to concern myself with this and I get on with my life again :D

Thank you for pointing me in the right direction plemans