Power cycle the router. Try to connect via ethernet cable from your pc to the router. Check your settings. If still no connection, most likely you will need to reset it to factory and reenter your settings.

One other thing to try is a different ethernet cable and ensure a good connection.

@ronif 

 

If the system light is flashing then that is a good sign, the router is operating normally.

 

Log into the router with a Ethernet cable like @ArcherC8 mentioned and look at the status. It might be that it simply lost the WAN IP address. If that status shows all 0's, leave the router alone and just reboot the modem. See if the internet comes back.