When I need to resintall my system or to fix my launcher I do this:
1) Cut "The Elder Scrolls Online" from inside "Program Files > Zenimax Online" folder and paste it in my desktop.
2) Uninstall the game.
3) Reinstall the launcher and carry on with it until the part where the blue buttom of the launcher says "INSTALL". Close the launcher DO NOT CLICK INSTALL.
4) Cut "The Elder Scrolls Online" from desktop and paste it back in "Program Files > Zenimax Online".
5) Open the launcher and give it five minutes to do any procedure then PLAY.
* Be sure the folder you copy is "The Elder Scrolls Online" and NOT "Elder Scrolls Online" from My Documents.