So you are attempting to create your own Moodle theme. Probably one of the first customisations we all want to do. However you now only see the “Clear Theme Cache) button an no themes listed. To verify the following solution, turn on debugging and see if this error measure occurs:
Fatal error: Cannot redeclare class theme_aardvark_lite_core_renderer in server_path_to_moodlemoodlethemeyour_new_themerenderers.php on line 3
Found a great post by Mary Evans that resolves this and summarise it here:
You got the Error message because you had duplicated the “Standard” theme, called it “Standard_1” and had not changed ALL the instances of “Standard” to “Standard_1”.
Solution: Clear theme cache button
When copying a theme there are a number of places where the original theme name appears, these are:
lang/en/theme_themename.php (where themename is the original theme name)
Check theme_themename.php as there will be a number of references to themename in there.
The error related to the renderers.php file because Moodle saw that it was duplicated, theme_Standard_core_renderer existed already!