WiFi doesn't show up as an option in my network folder. The Airport option shows my secure wireless network, but won't let me connect. What do I do?

I have an iBook, and WiFi doesn't show up as an option in my network folder. The Airport option shows my secure wireless network, but won't let me connect. What do I do? The manual won't download for the iBook's on my old PC, so I'm kind of stuck. A step by step how to solve this problem would be awesome! Thanks!