This story happened to a buddy of a friend of mine called Ben. Let's call him Ed.
Back in the days of VAX's they used to share disk drives using Hiearchial Storage Controllers that were very early versions of what is now known as RAID controllers. The collection of VAXes and HSC's were called a cluster.
An install of one of these clusters went bad when none of the VAX's could see the disk drives and that's when Ed was called in to see what's what. He pulled up his sleeves, dove into the OS code and was analyzing crash dumps to find out that the VAXes were not able to contact the HSC. So, with step one done, he jumped into debugging the code for the HSC and systematically traced the issue down to a bit which was not being set.
Follwing the wires, he chased the bit back to the control panel for the HSC to find out the bit reflected the state of the "On-line/Off-line" button. He pushed the button and everything worked.