my macbook actually can play sound thru the built in speakers... 2 mnths back.. i bought a altec lansing speakers and i pluck in the audio jack.... until today i take it out no sound come from the build in audio speakers... and the audio jack have red beam from the macbook.. i try going to the system prefernce to get it done.. but at the output section cant click... it stated no audio output...

and if i put the altec lansing speaker back... it became normal playing thru the speaker.. but i take out the speaker jack wanting to play thru built in speaker from the macbook... it didnt have any sound...