Hi Costa23, I have exactly the same problem with my Archer C9 starting this week, though it does occassionally connect to the internet for a few minutes at a time. I run my old Belkin router as an extension to the top of the house via an ethernet cable from my C9 and the Belkin allows me to connect to the internet continuously. If I connect my computer directly via an ethernet cable I get access to the internet so the problem is clearly a wifi problem. All my devices can can see my C9 and connect to it via the wifi.but I don't get any internet connection. I've updated the firmware to the latest version, switched it on and off and pressed the reset button but still no connection via wifi to the internet. Is this a comon problem?

My Archer C9 also just stopped working. I am currently directly connected to the modem as the router stopped sending a signal. My phones and TV can find my wifi but can not connect to it. Tried connecting the router directly to the computer to access the mytplinkwifi.net but I cant even access that. A little weird that multiply routers just stopped working at the same time.

First, reboot the router. Connect computer directly to the router via Ethernet, if internet works, then it's down to WiFi problem. Login tplinkwifi.net to change wifi settings, like SSID, password.
If no internet via Ethernet or WiFi, reset the router. Configure it again. After quick setup, check WAN IP address:
https://www.tp-link.com/en/faq-833.html
If no internet and cannot login the router, try the reboot and reset, change web browsers, use different devices. Check IP address on multiple devices, if none of them receive valid IP address from the router, it's probably dead.

My Archer C9, version 1, with the last firmware, and bought in july 2017, also stopped working today (april 3). What a coincidence!!!
I did everything vieldcs adviced. Nothing!!!

My old NEXXT Solaris 300 (US$30) that I bought 3 years ago is saving the situation. Incredible, a US $120 router worked less than a year. What a shame!!!

I had similar issues and found a solution.

My Archer C9 was showing the Red symbol for internet access.
No internet access through Wifi for phones or tablets but I could connect to internet with my laptop by connecting a cable to the router.

It turned out that my ISP had switched to CG-NAT and that was causing the issue.
Giving me a public IP solved everything.

Hope this can help others
/M