One thing you need to do is to modify your "troubleshooting" technique. Make it tighter is not always the best solution or sometimes as you have discovered any solution. If one works at a problem and is not able to solve it after a reasonable amount of time and effort then the first course of action is to throw out your previous assumptions and start over, thinking as logically as possible about possible causes and cures.

If that still fails then consult expert opinions or give it to someone else who is skilled at the task.