If you have no sound in Flash videos but in all other programs, there are two possibilities:
1. the PCM output is set to silence
* check volume setting with `alsamixer`
1. you might have a second audio device (e.g. a Webcam with a microphone) which gets preferred by ALSA
* fix it by unplugging it, or
* force ALSA to use another device, see [ALSA FAQ#26](http://alsa.opensrc.org/FAQ026)
* set *Skype* → *Options* → *Sound Devices* to *[ ] Allow Skype to automatically adjust my mixer levels*
1. some sound via PulseAudio is currently playing (see [ALSA → PulseAudio for Flash and others]({% post_url 2010-02-12-alsa-to-pulseaudio-for-flash %}))