EDIT:
1. Quit Skype
2. in finder
[yourusername]/LIbrary>Application Support>Skype>
shared.xml
open with textedit. (right click/control click to see the "Open With" pull-down)
3.search by hitting command-f and copy paste "
<VoiceEng>", with angle braces!
just below that make sure the line is
<AGC>0<AGC>, if it has a higher number, change it to "0", if it's not there, just insert it.
4. then save the file.
5. then reopen Skype
Taken from:
http://www.youtube.com/watch?v=NkSTFPDCk4k
ORIGINAL:
Can you delete posts? The one newer actually seems to be identical...
As far as skype, I stopped using it b/c it was bought by microsoft. I assume you're using version 5.xx? anyway... there seem to be TONS of people losing video/mic / both functionality on various versions of skype. It's often really helpful to post the
version of the software you're using, often posting which OS you're on is helpful as well (to people trying to help you, and therefore it helps you too).
found someone who has a similar issue (but noone replied):
http://community.skype.com/t5/Mac/Microphone-Issues/m-p/460595/highlight/true#M6429
and there are various comments here:
http://www.macupdate.com/app/mac/15805/skype
click on the troubleshooting tab to see what's up with that and not reviews (however, reviews often have info too).
For BASIC setup instructions you should VERIFY these settings:
https://support.skype.com/en-us/faq/FA10977/Sound-guide-Mac-OS-X-Lion
I have often used apps, including skype that would change the system settings when opened.