Hi Matthew,

Are you really, really, REALLY sure you're not sourcing too much current? I'm only asking because your problem sounds exactly what would happen if you forgot(or shorted) the limiting resistor.
I've forgotten to cut strips on a breadboard more than once. Try measuring the voltage on the pins, if it's not close to 5(or 0) volts you're in trouble. Between 1 and 4 is "out of bounds".

/Ingvar