Maintenance for the week of April 6:
• ESO Store and Account System for maintenance – April 8, 9:00AM EDT (13:00 UTC) - 6:00PM EDT (22:00 UTC)
We are currently investigating connection issues some players are having on the European megaservers. We will update as new information becomes available.
Don't click install. Wait. They know it's an issue, and they're resolving it.
Edit: If you're an idiot like me and clicked "Install" because you like shiny buttons, cancel the update and repair the launcher. That appeared to work for me.