@woozle Thanks for reply; I'll try (in next days) those steps you mentioned, have to say that it's very similar to what I already tried few times. I did not do the HW reset (with the button), will do...

Have brought the TL-WA850RE to relative, to install the Extender.Had good experience with TP-LINK. Unfortunately, this time, it's everything but good. Do not have access to the WiFi router at the...