tracert is a utility that traces a network route from point A to point B. I've used it to isolate my network issues. This may be helpful in diagnosing the 404.
Bring up a command prompt. At the prompt type: tracert
www.websitename.com and press enter. You should see some activity as it reports back to the command window. This data will tell you all the addresses, complete with how long it took to reach each point (and ultimately tell you where the request times out).
If you're running windows - to bring up the command prompt, click on "Start" then select "Run". Next, you'll see a dropdown list. In here, type "cmd" and press enter. At that point you should be cooking with gas.
PM me if you run into any hurdles or have further questions, sir.