I read this and it made me think of my methods of troubleshooting anything:
What I read...
1. Proceed logically!
2. Believe Your Evidence!
3. NEVER ASSUME ANYTHING! NEVER!!
4. Check Everything. You could have multiple faults!
Those are all good points to remember.
What I do...
ASK!!!
1. When did it work properly?
2. When did it stop working properly?
3. What was done in between those times?
I then proceed to Localize, Isolate, and Repair whatever it is I'm working on.
In dealing with computers I have found over the years that software problems
outweigh hardware problems by an outrageously enormous percentage.
I go very long periods of time where I never have to open a computer at all
to get at the problem.
Well, that's me.
What do you do any different? What do you think?

Inquiring minds want to know.