The router link LED won't turn on at all whether it is blinking, amber or solid green

hello! i guess it should be said that on my product (model) it says AC750 instead of N750 and nothing that says anything about "passthrough". However, on google images i can see that they have same looks at least, i'm not sure but i listed it as the model "EX3800|N750 Wifi Range Extender with Passthrough".

Anyways, my problem is that the router link LED on my range extender won't turn on no matter what. Power link LED and WPS link LED is functioning and have solid green. i have tried moving the range extender closer, so close that they almost thouched each other! clearly the problem isn't the range between the range extender and the router.

when i have tried to connect either way it says that the password/security key or whatever is wrong (it's actually not wrong since i can connect to the routers wifi, evidence is this message). when i tried connecting earlier the routers wifi said i couldn't conenct since "some information has changed since the last time you tried to connect". i was completely banned from internett, only with an Ethernet cable could i enter the internett. After a while i was allowed to enter internett again when having unplugged range extender for a while.

so now i sit here afraid of being banned by my own internett.

so to sum it up: i think the problem lies in the router link, but i'm not sure how to fix it, you should maybe also know that i'm a newbie when i comes to "these things"...