Ensure that the router's wireless service has been activated by you and that SSID broadcast is on. Check what that SSID is and change it if you wish.
 Ensure that all firewalls (those on the clients, not in the router) are either (a) running in their learning mode or (b) pre-configured with the details of the wireless LAN.
 Ensure that no adapter management software of any kind has been installed. Let Windows handle it.
 Ensure that the W-LAN adapter is switched on via whatever button or keyboard function it requires.
 Connect via the single PC-screen icon in the system tray. Browse for your network by refreshing the list and then select it.
 Enter your WPA-Pre Shared Key (assuming that you configured one, which you really need to).