I've had this problem for a while, and am not sure what to do about it. I also have Ubuntu (Linux) installed on my computer, so I can just boot to it and use the internet just fine. When in Windows, it says that I'm connected to the internet, but I can't use it (browse, or use any programs that need to access it). I can even successfully ping any website I want to on Windows 7, but obviously still can't access those websites. When I try to run "Remote Mouse," which is a program that lets you use your iphone as a mouse, it says something to the effect of, "Can't find or can't access the IP."
Since I had this problem for a while, I can't even begin to describe everything I've tried. Obviously, I looked up the proxy settings, and it's not that, as far as what I can see. Reset/re-installed network drivers, a lot more things.
Added (1). Thanks for the replies - Just wanted to add more details and clarify. I actually did the TCP/IP reset several times, without results. I'm also not using a laptop, it is a desktop, connected via Ethernet.