N300 Wifi Range Extender disables wifi

Thank you for your very thorough set of questions.

I have the WN3000RPv3 WiFi Range Extender.  My router is a Zytek PK5001z. 

My original quest was to have the tv be able to talk to my computer via wi-fi.  I plugged a wi-fi adaptor into the tv, and then added the tv to the network by pressing the WPS button on the router.  After this, I was able  to display photos from my computer on the tv.  At this time, my computer was attached to my router via an ethernet cable.

The next day, I realized that my computer was longer receiving internet signals via wi-fi.  I tried reconnecting my computer to the wi-fi by selecting the network and entering the password, but I received a message that I had entered the incorrect password.  I tried entering my password a few times to be certain, but I always received the same message.

After unplugging my tv, I reset the router.  After doing this, my computer was able to reconnect to the wi-fi.  I then went about adding the wi-fi range extender, which involved pressing the WPS button.  After doing so, I no longer had access to wi-fi.  When I try to connect to the network, I have gotten a couple of different messages, including that the password is incorrect, that some information has changed since the last time I connected and that additional information is needed to complete the connection, and a third one that I am not recalling.  

At the moment I have wi-fi access as I have reset my router again. But if I try to add the range extender, I get the same results.  Resetting the range extender did not change the results either.  Note that when I originally purchased the range extender (it's about five years old), it was enabled via the WPS button.  

I hope this is sufficient - I do very much appreciate you are volunteering your time.  But let me know if you still need further information.