Connection keeps quitting

I work on a PowerBook G4, and all of a sudden my wireless connection quits each time I put my G4 to sleep or shut it down. So when I restart, I have to manually enter my network name + WEP password. Any reason why it's doing this and how can I fix it? I checked in the System Preferences > Network, not sure what I need to be looking for.
Thanks ahead for any advice,
Zuwena