JavaScript half working in all browsers

Hi, I have problem with Java Script. Some JavaScripts are working, another scripts are working not. This problem is in all browsers (Chrome, Safari, Firefox). For example on page www.levelo.cz, there should be a slider with text in the middle of the page, but i can't see it - it doesn't display to me. I also often have problems with JavaScript lightboxes. I tried to reinstall system (without deleting files) but it didn't help.

Any tips? Thanks!