Starting WordPress in Safe mode
1. Navigate to [Information] menu on your site
2. Scroll down to Emergency Actions section

3. Check type of Safe mode deactivate all plugins and/or changing default theme.

4. Then click [Launch WordPress as safe mode] button.

5. Log in WordPress and check safe mode is working.
Plugins

No plugins are activated.
Themes

Default theme is activated (WordPress 4.9‘s default theme is TwentySeventeen)