Identifying the actual cause of a problem is the first step of a troubleshooting process. However, the first step of that first step should be verifying that there's a problem. Commonly, problems occur not long, if not immediately, after changes are made to the hardware or software. Or the user or stakeholder thinks that something happened, but can't recreate what they think they saw, heard, or smelled. To verify that a problem is real, recreate it—if possible—or take the time to question the user with open questions (ones that cannot have just yes or no as answers). Remember that a user, supervisor, or stakeholders don't usually have your knowledge or understanding of computer systems.
After you're sure that there is a problem, regardless of whether it's the one reported or another cause altogether, start the process...