Zkusil bych tedy zadat hlasitost mikrofonu ručně podle tohoto návodu:

Now you shall check your voice by doing Skype call <<echo123>>
Here you can monitor, record, (mirror) your own voice via VoIP.
Now check in
config.xml
You need to select "show hidden files" in folder options
To be found in
C:
Documents and Settings
Your profile name
Application Data
Skype
Skype User name

In CALL you shall find this entry
in line 6 it should look like this
<MicVolume>255</MicVolume>
255 is max volume - Value "0" and "256" are equal = mike volume OFF
Save
Restart Skype