Looks like the style.css code has become invalid due to multiple errors in the file. Some of the CSS in the css file were commented out incorrectly resulting in invalid CSS. Pls keep all custom changes to custom.css file or the Custom CSS tab in theme options and avoid modifying the style.css file.
The offending code are in line numbers 5468, 5478-5483, 5544-5546. Once you uncomment these lines and move the custom code to another file where you can manage things better, the slides will show up fine. If you have a copy of the original style.css, I would recommend replacing current one with the same.