Hi
In that case what is shown in System Preferences > Sound > Output and Input tabs ?
My iMac lists "Headphones" as the Output option (although it is actually External Speakers that are connected.).
My older G4/1Ghz Dual lists Internal Speaker, Line Out and can identify when Headphones are connected via the Front socket.
My iMac identifies three potential sources for a "Mic"
An External Logitech item I have, Line In (although nothing is connected) and the Internal Micophone.
If Changing the device (and potentially changing it back again to the plugged in device) does not change anything then navigate to Hard Drive/Library/Preferences/Audio and delete the two main .plists there.
(This is the Library at the hard Drive top level where you can see System, Users and Applications).
9:43 PM Friday; August 10, 2012
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously