Knock your network down to the simplest of configurations and then cycle bits and pieces in / out until you've either "cleared" all your hardware or found the source of the problem. Keep it simple and Occam's Razor and all that, right?
It's like a game of Clue. You just keep trying different combinations and making checkmarks until you figure out who killed who with what where. Once you figure that out, it's easier to address the problem. Tightening the nut on a bathroom faucet isn't going to fix the leaky shower, is it? ....sorry, I'm working on the bathroom today....
