First off - do you have PulseAudio running? If so, for HW/ALSA testing purposes, shut it down. Second, check your mixer settings to determine if your volume levels are appropriate. A great quick CLI app for this is alsamixer (media-sound/alsa-utils) - first start the alsasound service (sudo /etc/init.d/alsasound start), then run alsamixer - set your volumes to about 80%, and unmute all channels (use the 'm' key to toggle mute), then restart the alsasound service to save your volume levels (sudo /etc/init.d/alsasound restart), then add the alsasound service to your boot runlevel (sudo rc-update add alsasound boot). This will set it up to restore these volume levels on every startup (it will also save your *current* volume levels on every shutdown, so don't mute, shutdown, and expect to be unmuted after starting back up).

Now, double-check that PulseAudio is not running (ps -elf | grep -i pulse), and kill it if it is.

Then run:

aplay /usr/share/sounds/alsa/Front_Center.wav

If you hear sound - great, ALSA and your sound HW are working, and Flash audio will almost certainly start magically working. If not, please post the output of:

aplay -l

aplay -L

(both of those are L, first one lower case, second upper)

HTH-

James