Problems connecting to the Internet

Hi! I have been using the Microsoft Broadband Networking
(MSBN) utility for quite some time both at my home at my
school. Occasionally, I face a problem when I try to
connect to my school network. My Wireless adapter MN-520
is able to detect the network, but I'm not connected to
the Internet (as shown by the status of the MSBN utility).
When I check the adapter settings, the IP address assigned
is 0.0.0.0. The correct IP is assigned when I renew the
connection settings, but the internet is still
unavailable. I do not have any idea why the network
behaves so wierdly. Oddly enough, the connection goes
wrong when I want it to work the most. Can anyone please
suggest a way by which I can correct the problem?

Thanks in advance!