Hi! My Macbook Pro's sound suddenly stopped working earlier today. I was on YouTube and the sound was working perfectly fine, but when I went to another video the sound stopped working. I thought it may have just been the video itself so I clicked on another video. Again, no sound. I unplugged my ear buds and turned the volume up. No sound. I went to iTunes and tried to play some music. No sound. I thought that maybe my computer was too outdated so I did a software update and restarted my computer a few times. Each time I restarted the welcome sound DID appear. I don't know what's wrong! Does anybody know what's wrong and what I can do to fix it? That would be great. Thanks.