We had a user who could check email and do other network-related activities, but could not use Internet Explorer to do anything through a browser.
After much searching, I found the culprit:
In the TOOLS > INTERNET OPTIONS > CONNECTIONS > LAN SETTINGS section, the "Proxy Server" settings were set as shown above. Basically, the system was set up to us a proxy with no address.
How did this happen? The machine had been hit by malware. Once the malware was removed, this setting popped up as part of the "fix." If you are a tech, you may see this happen after cleaning a machine. Always check your browser to make sure you can get online following such a clean-up. If the machine cannot access web pages, check here!