I saved a slideshow to my computer, how do I edit it now?

I made a slideshow. In fact, it was so long, I burned it onto 2 cd's and their 1 hour long each. My question is, I saved the slideshow, both parts 1 and 2 onto my computer in the video section. I would like to post only the first 10 minutes of part one onto facebook. How do I shorten the video while it's on my computer and? It is no longer saved on Movie Maker, so I can't access it that way to shorten it  any longer. I just want to show family and friends a certain part of this slideshow and I'm pulling my hair out trying to figure out how I do that. It's probably something so simple, but I am not the most computer savvy person out there!