The 3v3 gpio pins and all of the numbered pins are not providing any voltage. Or rather, very little voltage. I used a voltmeter to check the voltage difference between 3v3 and ground and the needle moves very, very slightly.
I tested the diff between the 5v0 gpio pins and ground as well and they correctly provided 5 volts.
I think it may be short circuiting or something but I don't know how to test for that. It is also unlikely to be short circuiting in my breadboard as I am using an adafruit breakout board and I have nothing connected to any of the gpio pins.
If it is useful I have my RPi connected to a macbook with an ethernet cable and the main power is being supplied by a wall outlet - 5v micro usb.
(I have a RPi model B)