OK here is my problem

I have a computer in my house that is networked via wireless usb device (linksys) - my main pc has the wireless router.

Recently the computer that always connected wireless stopped internet connection so i figured it was the wireless adapter since it was pretty old. I bought a new wireless adapter and same thing. The computer is able to connect to the network fine but it will not have internet access. I tried numerous things such as

reinstalling network adapter
re-configuring router settings
changed WEP key and made sure correct one was entered

The weird thing is... The computer reads the router fine and shows an excellent signal (100%) from the command prompt I pinged the router and all attempts were sucessful but if I ping yahoo.com it failed (thus no internet connection on it)

I called Linksys and they had NO idea.... they kept telling me that there must be a problem with my router but I also have a laptop in the house that is able to go online wireless with no problem.

The one thing i did notice is that if i tried a repair of the wireless network it does get hung up and reports it is unable to renew the IP address. In the settings we have the IP configured as automatic and linksys even tried a manual setting and it still didnt work.

Firewall is disabled and the only new software on computer is PC Doctor which scans for malware and trojans which i also tried disabling in addition to all virus programs.

Both main computer and one setup with wireless adapter are using Windows XP and the laptop (which has no problems) is using Vista Home

Any help would be appreciated