MN-500 base station question

I'm trying to set up my base station. It was previously
set up and worked fine. I'm reinstalling it and my all
three lights are on on top, all lights are on my external
modem, and my notebook wireless adapter is working fine,
as I am e-mailing from my notebook. When I turn my main
computer off, my port 1 lights up like the base station
is ready. When I turned on my main computer, the port 1
light goes off and I cannot get on the internet. Does
anyone know why this is happening or what I can do?
Again, my network adapter on the notebook is fine, it's
just I cannot get on the internet with the base station
computer. Thanks for any info.