Maintenance for the week of March 16:
• [IN PROGRESS] ESO Store and Account System for maintenance – March 18, 6:00AM EDT (10:00 UTC) - 4:00PM EDT (20:00 UTC)
Is it giving you an error number when this happens? If it's Fatal Error 11, this can be due to corrupt game files during installation. You should be able to resolve it by repairing your game client from your launcher.