Although I'm not a regular Skype user, I still employ it from time to time to do my share of VoIP. But it happens quite often that I don't get any audio from my microphone, although incoming sound works just fine and all the alsamixer switches and gains are set properly. But, on both of my Intel HD Audio equipped laptops this trick seems to solve the audio capture problem just fine:

First, open a terminal and do a

sudo alsactl store

Then open /var/lib/alsa/asound.state in an editor (you'll need super-user privileges, a sudo nano /var/lib/alsa/asound.state in the same terminal you used for the last step will do) and look for something like:

control.12 {
        comment.access 'read write'
        comment.type BOOLEAN
        comment.count 2
        iface MIXER
        name 'Capture Switch'
        value.0 false
        value.1 false
}

The numbers might differ, but the name 'Capture Switch' line is a clear indicator that you've found the right control. Once you find it, change the two value lines to true, so you end up with

value.0 true
value.1 true

Then, Ctrl-O to save your file and then Ctrl-X to exit nano (just save the file if you're using a different editor). Back to the console for a final command:

sudo alsactl restore

Now you're free to ring up echo123 and test out your new settings. Hope it helps!