After installing Fedora 13 on my desktop PC and laptop, I found that audio was extremely silent on the desktop. Everything worked fine using Fedora 12. Apparently for some reason the only available soundcard is for not set as default as it should be, and it's master volume is set to 0%.
This can be changed by running
on a terminal, it's the first regulator on the left. However, the setting is reset to 0 on each reboot, so I've added a amixer command to my startup applications:
Click System -> Preferences -> Startup Applications and add
amixer -c0 sset 'Master Front',0 80%
Since I've wasted an entire afternoon on finding a fix, I decided to post it here, hope it helps.