Are the regulators oriented correctly with the diagram on the PCB? If they're correct, you can check the in and out voltages on the regulators.
With the board oriented so that the pixelnet universe selection jumpers are at the top of the board, the 7805 should have 12V across the left two pins (positive on left, ground in middle). There should be 5V across the right two pins on the 7805 (ground in middle, positive on right).
The LD1117C should have 12V across the left and right pins (ground on left, positive on right). There should be 3.3V across the left two pins (ground on left, positive in middle).
If you're getting all the right voltages on those, then it could be you just have the LED in backwards. You can check for power at the LED itself to confirm.
