All video runs real fast with no audio

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http://forums.fedoraforum.org – In Firefox, Midori and Chrome all video runs at super high speed with no audio. Here are some example videos: EndangLang, WhatNew, Html5, YouTube. I also tried to view a DVD with MPlayer. Same problem. The [ and ] keys speed it up and slow it down as usual, but when it says it's at 1.00, it's moving fast. Speed 0.20 looks roughly normal, but there's still no sound. I first noticed this about a week ago, but I hadn't tried to run any video on this PC for maybe a month or two. What can cause this? What can I try? uname -a Linux xxxxx 3.4.3-1.fc17.x86_64 #1 SMP Mon Jun 18 19:53: (HowTos)