The symptoms are as follows:
I can access wireless networks, and my network and sharing center shows that I am connected to the Internet, and have an IP Adress, DNS server, DHCP server, and so on. Using the command window, I can ping most websites, including www.google.com, www.wikipedia.org, www.yahoo.com, etc. Using Internet Explorer, however, I can bring up almost no websites. Many websites that I type into the address bar, such as www.google.com, return a search result for "www.google.com" in my default search engine instead of the actual site. This happens for other websites as well (e.g., www.yahoo.com). If I click on the wikipedia article for google returned by the search engine, I can actually open that article in Internet Explorer (at https://secure.wikim.../en/wiki/Google). But that is pretty much the only website that I have found that will be returned (except the search engine results). Generally, all websites typed into the address bar return either a search engine search for that webpage, or the error "Internet Explorer cannot display the webpage". This includes websites that I can successfully ping with the command window (such as www.google.com, www.yahoo.com, etc.).
Windows Defender cannot reach the Internet to update definitions, Windows Update cannot reach the Internet to download updates, but my anti-virus program - AVG 2011 free edition - does manage to get to its server and download updates. I did a scan with AVG for viruses and rootkits, and found nothing. However, I did get an automatic pop-up yesterday (Nov. 19 2010) that a trojan horse was found upon opening Windows Defender (if I remember correctly), but have seen no other virus warnings in conjunction with this issue.
Any and all help is appreciated. Please let me know what to do to correct this problem.