Curiosity Killed the Mac

The speakers won't boot?

From what I gather, it sounds like your Mac thinks that the headphones are still plugged into the Mac.

There is actually some sort of switch in the jack causing the red light. I don't know much more than that. I'm sure someone will be along shortly with more details...

The red light being on means the computer thinks the jack is occupied, and is transmitting the optical audio signal through the jack.

If you take a thin wooden toothpick or bobby pin, you may be able to pop the little switch in there to get it back to the "unoccupied" position. Reading around tells me to aim for the left side of the port, unless that's changed since the last gen of MacBookPro. You can also try tapping under the port as you do this to help jostle the trigger.

take your headphones and plug them in and out until no red light