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Unholy 'Hosts' File Hang-Up

My desktop PC won't access such Web sites as www.weather.com, www.newyorktimes.com, and even www.microsoft.com, no matter which browser I use. I get the standard 'The page cannot be displayed...' message. Oddly, I can get into some inaccessible sites if I drop the 'www' from the address. It isn't a phone-line or ISP problem because I can get in when I dial into the same account using the same line from another computer. Someone suggested that I reinstall Windows. Is there an easier fix?

Seth Shaw, Colebrook, Connecticut

Your problem could stem from other causes, but everything you mention points to a Hosts file gone awry. Back before the Web, computers needed the Hosts file to correlate domain names such as 'pcworld.com' with the numeric IP addresses that allow data to move from one machine to another over the Internet.

Internet service providers and office network administrators now use Domain Name System servers to track the ever-changing domains and their associated IP addresses. The Hosts file remains on PCs, however, enabling us to inadvertently mangle our Internet access by adding addresses to the file, and letting Internet utility authors bypass sometimes-poky DNS servers to speed Web-site access. My guess is that you're a victim of the latter.

The problem is that a domain's IP address tends to change over time. If you don't regularly update your speed-up utility, the out-of-date address mappings listed in the Hosts file prevent access to the domain. Meanwhile, the DNS server continues to handle domains not listed in Hosts, which explains why you can get to some sites but not to others.

Remedying the problem is easy: Search your hard disk (using Start, Find or Start, Search) for a file called 'hosts' (don't enter an extension). The only entry not starting with '#' should be '127.0.0.1 localhost' (see Figure 2); if there are other lines without '#', delete them. Or if you want to avoid editing the file, rename it something like 'hosts.bak'--and forget about it.