Slider content disappeared (Grading theme)

Hi. I’m completely new to WordPress, as well as CSS, and I need a bit of help.

I have the Grading theme installed on my blog. I modified the theme a little to fit the feel of the site; however, 95% of the coding remains the same. The only file I altered was the style.css file.

Up until a while ago everything was working perfectly: the slider images displayed properly next to a preview of the featured post’s contents. None of the links are broken – the images are sourced in Editor and everything. But for some reason, the preview text no longer shows up on top of the slider background, and neither do the slider images.

The blog started off in WordPress 3.2.1, but I upgraded to 3.3.1 a couple weeks ago. Since then, all the slider content has disappeared. I read elsewhere that it might be a problem with incompatible plugins, so I deactivated and deleted the ones that came with the site as well as any new plugins I had downloaded. That did absolutely nothing, so I downgraded back to 3.2.1. So far, it hasn’t changed anything.

I know nothing about PHP, so if that’s the problem here, then I have no idea what to do. :/ Would greatly appreciate some help. Thanks!