Airport Extreme problems with Mac

[Jiggymike]

For as long as I've had my computer (close to three years, it is a G4 Mac Powerbook), I've used the same airport base station and WPA personal network. I've never had any extended problems with it in that time span. However, as of last week or so, I am no longer able to use it to connect to the internet. I connect to the network, which has full signal strength and says I am connected to the internet through Ethernet (wireless). But when I try to use any internet application, it just stalls and doesn't connect. Currently I am using some unsecured network in my building and the internet works just fine as long as the signal strenght is greater than one or two bars.

I have also had trouble recently with my built-in ethernet. When I plug it in at school, it often does not even show up in my network settings. When it does show up, it sometimes says that it cannot detect any networks, even though the ehternet wire is plugged into the jack. I am wondering if maybe these two are related. Thanks ahead of time for any help.