Editing Video on Quicktime Pro for Windows 8 and keep getting "Quicktime is not responding"

I've been trying to edit some high def video and I keep getting "program is not responding" messages as I near the end of the video. Has anyone else experienced this problem? It just sits there unresponsive for hours and then I finally give up and just close the program. I have the latest version of the software, but don't know what else to check so that I'm sure I have everything setup properly to use. Please help.