The 404 or Not Found error message is a HTTP standard response code indicating that the client was able to communicate with the server, but the server could not find what was requested. ie: connection to the destination server could not be made at all. Your computer is able to connect to your ISP server but the ISP server is not able to connect to the website you had requested.But the requested resource may be available again in the future.
It can also be the reason that Papauz has mentioned
Depends where you were trying to go but for examply the Veterans Administration web site MyHealthyVet was under maintenance Sunday and was throwing up all kinds of errors.
Can you post a link here -- not to a file download but to a website -- where you are getting this error?
PS Please don't try to put all of your problem in the Subject heading .... if you did write details in the message area and they did not appear then please try Compatability View on your browser.
404 errors mean on webpages that the page you would like to see is not present on the server, aka the html file is removed, renamed, etc. It's the same like when you uninstall a program, but the icon remains on the desktop. You tries to run it, but you will only got a search window as the program is missing.