Well what version of OS X are you using? Do you have any Airport wireless card in your Mac Pro?
Plus go to System Preferences->Network. There highlight (in the left hand column) Airport. Then if the left hand column, at the top use the pull down 'Location' and make a new location (calling it anything you want, link "Home Wireless"). Then try the wireless connection (selecting the proper wireless security that everyone else is) again. See if that works.