Do you mean you cannot log on to the router or to a specific site such as TPLINK.Com. If it is the router, I have had issues signing on time to time on my Archer C8. Sometimes http://tplinklogin.net/ will fail where http://192.168.0.1/ will work or the other way around. you can also connect with tplinkwifi.net via WIFI. Some routers default to 192.168.1.1 (see label on your router). It can be changed in the settings but best if left alone. For WIFI you may be able to use the TP-Link tether app. Also powering down both the router and your PC and back up may help. Also clearing your browser history, cookies, and such may help. You can also try a different browser. If you get the sign on page, use the default userid and password for the router. If it has changed and you do not know the userid and password, you will need to reset the router back to the factory settings and re-enter all of your settings.