Updated: December 1, 2014
The problem you are facing is as follows. You are using Skype on Linux. Until recently, everything has been working fine, and you had audio and video, without any problems. Then, suddenly, following an upgrade to Skype 4.3, you no longer get any sound.
This little tutorial will help you understand the scope of the problem and how to fix it. Of course, your issue might be completely unrelated, but I believe this guide will give you some really decent pointers and lead you toward a resolution. Please follow me.
Anyhow, you have Skype running, but there's no sound, not even the test call. At this point, you will be inclined to hit the search engines and start checking random forum posts and other articles, all of which will suggest ever so slightly different workaround, and which you will be applying with an increasing degree of frustration.
My suggestion is to start slowly and then expand. First, open the Skype options. Then, under Sound Devices, check how the Microphone, Speakers and Ringing are configured. What do you see in the drop down menu? If you see Virtual Device, then you have a problem. But the question is why? It used to work before.
The answer is, in version 4.3, Skype dropped support for ALSA, so if your distro is using ALSA, you no longer have sound support. You will have to switch to a different sound framework, like PulseAudio. Furthermore, Skype is a 32-bit application, and if you are running a 64-bit distro, then you might be missing some of the core libraries required to get the program working. You can always check that using the ldd command, as outline in my hacking tutorials. More links further below.
In my case, I encountered the issue on Linux Mint 17 64-bit. Indeed, the symptoms are as above. Fortunately, the fix is rather simple. You will have to install a single missing 32-bit shared library, which is not included in the dependencies.
sudo apt-get install libpulse0:i386
Once you install this package, restart Skype. Now, under the sound options, you will see PulseAudio (local), which is how it should be, and you will have your sound back. This means you need not hack your system, do any command line tweaks or install a whole bunch of tools and frontends for managing your sound. Remember, everything used to work, so the change is minimal.
You might also be lucky and not be having this problem. For example. Ubuntu escapes this issue. But please be aware of the small differences and nuances between distributions, so that you do not end up chasing ghosts. And there you are.
To help you max the inner geek in you, read all of these:
Missing 32-bit software on 64-bit systems
Skype setup on Ubuntu
There we go, a simple and quick tutorial. But there's more to it than just installing a missing library. I want you to be able to think and understand your problems to the core, so that you can drive toward an efficient solution. In this case, an application changed and it no longer works. So what could have gone wrong?
The first piece is to figure out how sound is configured in the program. Once you realize the problem is in that area, the solution is much easier to find. Then, 32-bit software, 64-bit system, it's a big clue. And so we have our sound back. I hope you liked it.