Wireless and networking issues

I have set up a wireless laptop down stairs. the router and the pc are upstairs the pc is on xp and the laptop vista. Sometimes out of the blue the laptop reverts to local internet connection. Usually I can solve this by pressing the wi-fi button on the laptop. This does not always work. Anyone know why this is happening or how to resolve it.

Also on the laptops network the xp pc upstairs does not always show up. If I turn on the xbox the xp pc will show up.

Go to tools, internet options, connections and select never dial a connection.

Just tried that there. It was set to that by default but thanks anyway.