SparkFun Troubleshooting Tips
Contributors: bboyhoFavorited Favorite 7
Check, Test and Recheck
Maybe you rushed through a step. Try checking back through the troubleshooting checklist. Or maybe your assumption was wrong? Check your assumptions. While rare, it's possible that there is something on the board that is bad (e.g., tombstoned SMD components, insufficient solder or a bad PCB).
Even turning the circuit off and coming back at another time will help in troubleshooting the problem with a different approach.