connecting computer to network

Hello,

I set up a network at the office to have a secure internet connection. I have 6 computers running windows 7 and 1 laptop running XP. When I viewed available wireless networks all these found the network and asked for security key. Once entered all work perfectly. I have 1 other PC running XP that shows I am connected but I cannot access any website (access linited). On this machine I never got the prompt to enter security key. If someone could walk me through this I would greatly appreciate it.

Thanks