Audio connector red light problem.

#1 The red light in the headphone jack means that the MacBook Pro thinks that an optical audio cable is plugged into the port. Try unplugging and replugging a headphone plug into the port several times. There is a tiny sensor inside the port that determines whether the port operates in optical or analog mode. Plugging something analog in is supposed to trigger the sensor and restore the analog signal.

#2 Your digital audio out has switched on. You can insert a plastic toothpick in the hole and try and switch it off. The switch should be at the 3 o'clock position and go towards the 6 o'clock position. Some people also have had luck inserting their headphone jack and pulling out a few times. Another recent report was that inserting the headphone jack and turning it in the hole helped.