First we need to see what kind of issue is present. Upload led_test.ino and see if your compass works.
If your compass shows a set of four LEDs rotating to each quadrant, then we know your hardware is working fine. This means that the problem is most likely in your sketch. Go to the Software Issues step for help troubleshooting your code.
If your compass does NOT show a set of four LEDs rotating to each quadrant, then you need to fix your hardware. Go to the Hardware Issues step for help troubleshooting your electrical connections.
If the sketch doesn't upload at all, try consulting our General Help page.
The best advice to give on software problems is just to check everything. The error messages Arduino gives when verifying code can be cryptic sometimes. Go to each step in the Software block and look at the Help section in each step. Make sure you followed each step exactly, copying each snippet of code as instructed and pasting it in the appropriate location. If you still cannot find your issue, try going to our Forum for help.
If only some LEDs work but others don't, try looking for a short circuit. A short circuit (or just 'short') is when you have wires in your circuit that touch but aren't supposed to. In this case, shorts are likely to occur where you solder. Check the bottom of your compass shield to see if any LED or resistor leads have too much solder on them. If you notice a short, use your soldering iron to heat up it up and draw some solder out.
If the Arduino won't turn on, first try replacing your batteries. Also try checking the connection between your battery pack and Arduino.
Below is the schematic of the compass printed circuit board.
The Compass PCB Schematic