You're fixing a desktop PC that's behaving strangely. What step should you take to build a theory of probable cause as part of best practice problem-solving methodology?

External or internal research based on symptoms is part of developing a theory of possible cause. The following are the steps in CompTIA's best practice methodology for problem resolution:
1. Identify the issue.
2. Develop a theory of likely cause (question the obvious).
3. Put the theory to the test to determine the cause.
4. Create a plan of action to tackle the problem and put it into action.
5. Verify complete system functionality and, if necessary, apply preventive actions.
6. Keep a record of the findings, actions, and outcomes.