Following the schematic (it's in the WIKI), power comes in at the power connector, goes thru the single supply jumper, diode D1, and the LD1117 regulator. From there, the 3.3v is distributed around the board.
Using your meter, check the middle and right lead of the regulator. The middle (and metal tab) is the 3.3v output and the right lead (when looking at it with the leads down and the writing visible) should be your supply voltage less about 0.4V due to the diode.
If pin 3 shows no voltage, check the single supply jumper and D1 - if D1 is in backwards, it will block the power. You can jumper around D1 to check; it's job is to protect the board if you hook power up backwards.
If pin 3 shows voltage but pin 2 doesn't, it's either a bad regulator or 3.3v is shorted to ground somewhere on the board.
/mike