PROBLEM CONNECTING TO FRIENDS WIFI?

[M S]

I have a emachine laptop running windows vista.
In the past week I have tried to connect to two different wifi connections but was unable to do so despite the fact that I have used both several times before and normally just turn on computer and it connects automatically. On one of them it did not even show up the connection althoug it did work fine when I connected with a cable.
Wifi works fine when I am at home so am wondering if it could maybe be something in settings which has changed.
Please help !
thanks for answering but can you please explain what "wifi card failing " means and what I can do about it.

[tumbleweed_biff]

Unless you changed the settings, then that wouldn't be it. More likely the WiFi card has failed you.