Since those two computers can connect to internet though wireless, your wireless AP is working well, both hardware and software settings. You can try to set the IP, getway, NDS, SSID and authorization manually on that troubling computer. Allow the wireless to go though the firewall and not get blocked as well.
I have a D-655 wireless router connected to my iMac main computer. We have 3 computers connected to our home network. My daughter's laptop and the main computer is connecting to internet just fine. Mine isn't. Home network is showing on available network connections and signal strength is high. Diagnostics says problem with wireless adapter access point. It also says network cable unplugged but it's wireless so that doesn't make sense. I am on Windows 7, Dell.