Maintenance for the week of October 6:
• [COMPLETE] ESO Store and Account System for maintenance – October 7, 6:00AM EDT (10:00 UTC) - 4:00PM EDT (20:00 UTC)
You could be running into a connection issue preventing you from logging into ESO. If you continue to receive the message "Unable to connect to game server" when logging in you can go through the troubleshooting steps in the help article linked below.