Well, let me tell you, I ran your code and it worked perfectly.
Mind you, I tried it on a 16 MHz Pro Mini (clone) at 5V (and used a LED with resistor as indicator, but also tried just testing with a meter). You mention 3.3V - you are not perchance attempting to run a 16MHz board at 3.3V are you?
The missing information - what else have you done successfully with this arrangement?