Try temporarily turning off the security settings on your WiFi router (make it an OPEN network) and see what happens. If the problem device connects to an open network then go back and review your security settings on both the router and the problem device. Is your WiFi router set up to supply a sufficient number of IP addresses for all of your WiFi devices? Some routers are set-up to dole out IP addresses within a specific range, exceed the number of addresses available and the last device to try to connect may not be assigned an IP address by your router and thereforee will not be connected . Let us know if you come up with an answer.