Why did my site crash when I moved module and theme folders?
Drupal keeps an extensive cache of all functions in (contrib) modules and the files in which those functions can be found. Since you moved the files, Drupal is probably attempting to call a function from a file that is no longer there. (It should have thrown a more detailed error in your webserver log.)

Steps to repair could be to move the files back to their original position (Drupal works fine without contrib and custom folders, but it might be easier for yourself). Or enter the database and attempt to empty all tables that end in _cache. That should make Drupal reïndex the functions.