Vista Internet Connection Problem

Hi. Ive been trying to help a friend w/ his computer. He bought a Gateway w/ Vista Home had it hooked up at his house wired to a router. Had no problems. Hes not sure what happened but all of a sudden he cant view any web pages. So I now have his computer and I have the same problem. It is wired directly to the router. Its connected to the internet and my home network. I can do things like windows update or ad aware updates, I can access anything Im sharing on my network but I cant surf the internet. Ive tried IE7 and FireFox2. They both just say your page cant be displayed it doesnt think there is a connection but I got through and everything says connected. Im typing this on my own computer running XP and my wireless also works so I know it wasnt just a problem at his house. Ive searched online and tried what they have said but nothing has worked. I thing I keep seeing to try is change the "IPv4 Checksum" under the device manager but I dont have that. Its an intel based nic and thats not listed under the properties. Any more help or suggestions would be appreciated. He doesnt care if I reformat but I dont think I should have to and Im also afraid that might not solve the problem.
Please help.
Thanks Matt