Restarted the MBP again and now it does recognize the headphones again, and everything seems to be back to normal. Then plugged in my headphones and to my surprise wasn't recognized. iTunes also worked again, internal speakers. I restarted the computer and I noticed the sound icon in the right top corner was back again.
What did work for me was to run Apple Hardware Test (restart while keepin 'D' on the keyboard pressed. The exact same images as the topicstarter posted aplied to my MBP.
It was just a little bump on the side where you can insert DVD's and it could've been I already didn't have sound before that but didn't notice because I mute my sound often. My MBP had a little drop of the couch wich might've triggered the condition, although I'm not sure. Only I didn't have the start-up sound when I rebooted, so no sound at all. Macbook Pro (15' model with trackpad, and 4GB RAM). I had the exact same thing as the topic starter.
