Finally, keep calm. Your network does not have a mind of its own. If you take a logical and organized approach to finding the cause of a network problem, you will probably solve the problem without developing (or enlarging) an ulcer. Over time, you will recognize particular symptoms and know how to home in on the most effective diagnostic tools and techniques.
If you can't find the problem after searching for an hour, walk away for a few minutes. Make yourself a sandwich, have a cup of coffee or a glass of lemonade, or go for a short walk. The network will still be there when you get back, and you'll feel better about it. Approaching the problem with a fresh mind can often be the most effective possible way to solve it.