Audio file keeps moving over a video file where I don't want the Audio.

I have a video near the end of the show that I do not want the audio to be.  I then have 2 slides that end the show that I keep trying to add audio to.  The audio is there but it keeps sliding over to the left of the slides that I want the audio to be.  If I try to select the slides at the end to sync to the audio file, then the audio file for the slides just before the video slides over to the right to the video slide.  I have tried to find a fix for this and it is very frustrating.  I hope I have explained this so it is clear.  Thanks for any help in this matter.