Rendering problems

I recently got back into the video editing community after recovering my computer from a virus. I ended up getting the newest version of Movie Maker and began to edit it. Everything was fine until I began to render it so I could post it on YouTube; all of my clips weren't lined up with the music at all. I went back and edited them again so they would be lined up. Then when I rendered again, I had same problem. I did this about three times and still the same result. Can someone explain what is happening and how I can fix it? I've been editing for four years on three different programs and NEVER had this problem.