Once you fully define the problem or problems, begin creating a troubleshooting plan. The plan should list all possible causes of the problems that you can think of, and how to test for each cause.
The plan will act as a checklist so that you know what you have tried and what is left to check. The checklist is helpful if more than one person will be troubleshooting: without a written plan, people can become easily confused and steps skipped. Also, if you have to pass the problem-solving to someone else, providing a detailed list of what data you gathered and what solutions you tried demonstrates professionalism.
Be ready to add steps to your plan as needed. After you are part way through, you may discover that you overlooked some tests, or a test you performed discovered new information. This is normal.
Make sure your administrator account has the permissions you need to run all diagnostic tests and to make configuration changes. Also, you may need access to other networking equipment such as switches, routers, and servers to help you test. If you do not normally have access to this equipment, contact your network administrator for assistance.