I have a desktop PC hooked up to an ethernet cable. I was surfing the web one day when the internet cut out and I haven't been able to get it back since. This was in Windows 7. I have two hard drives. The first has Windows 7 on it, and the second has Windows XP on it. When I load up the Windows XP drive, the internet works great. But, when I start the 7 drive, there's no possible way to connect to the internet. I don't understand it. I have the ethernet cable [that is usually in the PC] plugged into my laptop (running WINDOWS 7 of all things). I'm typing this from the laptop, and the internet works perfectly on it. I don't know what to do about this. I'll provide any more info needed.
At least we know it's not hardware, that cuts out a lot of guessing.
I'd start by downloading the 7 drivers from the XP drive and manually reinstalling them. Next guess, would be that a Windows Update has created a conflict. You may want to review recent updates, and uninstall IF it appears that an update is to blame.