Alright, I am not very experienced working with Windows Vista, and I'm having serious trouble solving this problem. I've been searching for solutions for two days and not found anything that works. The computer is a Compaq Presario A900 running Windows Vista Ultimate (Service Pack 2). My brother used the computer's wireless internet connection for four years without problems, but lost all internet access when he returned home a couple months ago. The computer will connect to any network, but has the message "Unidentified Network - Access: Local Only". The computer first had the problem trying to connect to the Internet through an iPhone's Wifi connection. It happened again on the wireless network at my home. I took the computer to work to test it with a wired connection and had the same result. I originally thought this was only a wireless problem and completely uninstalled and reinstalled the Atheros wireless card drivers. I have completely disabled the Windows Firewall and removed all Anti-Virus (Avira free was installed - Norton is not on the computer). I have tried Safe Mode with Networking, and it does not fix the problem. I ran a Fix-It yesterday that was supposed to fix specific registry errors, but that did not solve the problem either. I also found a solution on this website that involved enabling sharing. One user said it fixed the problem, but it did not solve it for me. The only thing I am certain of is that this cannot be a problem with the router. All three places I have connected have various other computers connected constantly: The iPhone regularly connects a different Windows Vista-powered laptop, Windows XP Desktop, and Windows 7 netbook to the Internet. My wireless router successully connects a Windows XP Desktop, Windows 7 laptop, and Macbook. Obviously, the wired connection at work successfully connects over a dozen computers. I'm out of ideas on this one...thanks.

That is very weird... There is one thing that i can think of other than reinstalling. Go to the services.msc and look for DHCP Client. See if it is started. If not, then start it. If you could post the output of ipconfig /all it might help find a better solution other than reinstalling.