I had powered Altec Lansing speakers hooked up to my 24" iMac and they worked fine for ~1 year. I recently upgraded my RAM with no difficulty, however afterwards, the headphone jack no longer recognized the presence of the external speakers. The sound preferences panel "output" tab shows "Internal Speakers" and "Built-in Output" regardless of whether the external speakers are plugged in or not. Rarely and for a moment, if I plug and unplug the speakers from the headphone jack, the sound panel occasionally shows "Digital Out" but still no sound and it quickly reverts back to "Internal Speakers." Any thoughts?