If you don't want to spend time on troubleshooting the problem. Do a hard reset on the router to get it back to a known working configuration. This should return the IP to the default as printed in the manual, turn on the wifi with the security key printed on the label(if there is one), and turn on DHCP. Log in via ethernet with the default username and password as printed in the manual. Then change the default login password and reprovision the router to your needs.