@Misa0014sk Follow the instructions in this post to reset your router to factory defaults and configure a new password.

@pissedoff2 Try the suggestions in this video and see if that helps.

@I-Am-Iron-Mam What's the make and model of your modem ? If it's a modem only device, then your question has been answered by @Philbert. But if you have a modem router device, which works in NAT...

@MrMan987 Make sure you're with the latest FW release for TL-WR902AC - here. If TL-WR90AC works with a shorter cable connected to your main router, your issue probably is with the long ethernet cable...

@Zubair_bd No, you can't have a custom messgae from the router regarding blocked websites.

@Zubair_bd You can try using Access Control instead to restrict visiting a particular URLs. Here's the Access Control configuration guide for Archer C20.