While my computer speaker is working fine, any of the videos I watch using Safari are not making any sound, they are muted and I do not know how I did this. Videos from Youtube or any quicktime movie just won't play sound.
First thing to check is the volume in QuickTime. When you load up a QuickTime video, there's a little pull-down slider that controls QuickTime's volume. Is it set all the way to the bottom? If it is, that explains your lack of sound.