is associated with a numerical address like 216.158.54.197
The URLs are registered and there are master "dictionaries" in which one can look up a URL like "
http://democraticunderrground.com" and find out it means something like "216.158.54.197"
Unfortunately, there are several standards for the numerical names, and not all DNS servers support all the standards. This was a problem for me several months ago, because for the version of OSX I had on my Mac the machine would try to obtain the most modern standard repeatedly before trying to obtain an earlier but more common standard: with webpages having multiple links to other URLs for content, this slowed browsing to a crawl and resulted in multiple claims webpages weren't available (actually because the effort to load them had timed out). I don't know whether this has been a problem on other operating systems. On a Mac, it's easy to add a new DNS in System Preferences > Network > Advanced > DNS Servers. I don't know about other operating systems. I did get an immediate improvement by adding an OpenDNS server address like 208.67.222.222 to the list, but the real solution was to update the OS after Apple fixed the bug
A few other questions you might ask and things you might try:
Does your ISP offer different sorts of accounts, such as "safe browsing" options? Did you accidently change an account option?
Do you use the same browser for home & work? Are the browser settings the same? Have you tried using different browsers? (I have seven different browsers installed currently, some of which I simply don't use and should probably uninstall, others of which I use intermittantly for different purposes. I don't have IE installed, but some webpages generally don't work except with IE: I don't like IE, and don't have it installed, but some other modern browsers can supposedly pretend to be IE well enough to load some of those pages; I haven't had that problem, but at least I have something to try as a work-around if I encounter it)