There's not one if you didn't set one up. The codex has a good example of how to do this.
* This will log all errors notices and warnings to a file called debug.log in
* wp-content (if Apache does not have write permission, you may need to create
* the file first and set the appropriate permissions (i.e. use 666) )
White screen of death is usually caused by WordPress looking for the active theme and not finding it. If you can access the admin area, got to Appearance > Themes and reactivate your theme.