connecting powerbook G4 to linksys router

[Elizabeth]

I am trying to connect my powerbook G4 to a linksys wireless router. I have completed the airport setup assistant, and the wireless icon on my desktop shows linksys with a checkmark next to it-- but it says that the signal is unavailable. When I try to connect to the internet it says "specified server could not be found." After speaking with tech support, I completed a power cycle, and was able to connect for two minutes. As soon as I went into another room however, I lost the connection and couldn't get it back. Please help! I'm so frustrated!