Well actually a couple of people try to help me, but it didn't work. The reason why my files didn't work was the voice files had been recorded as wam files and they had to be wav files. I actually had to convert each of them and re-attached them. Not all your sound aren't working. You need to chek if the sound file is "contain in presentation" which means it has been embedded. All you slides up to banana work. The way you can check if they are link or contain in presentation is the following:
Determine if a sound is linked or embeddedIn Normal view, click the sound icon on the slide that you want to determine the linked or embedded status for.
Under Sound Tools, on the Options tab, in the Sound Options group, click the Dialog Box Launcher.
Under Information, next to File, you see either [Contained in presentation] (meaning that the sound is embedded) or the path to the sound (meaning that the sound is linked).
Even though I deleted all the files and attached them again until I converted them into wav files, they didn't work.
To convert files easily you can go to:
http://media-convert.com/Hope this helps!