up2date and yum not working?

Hi,

I have a fc1 linux system.  A few days ago, I changed its hostname and ip
address from a test system to a normal system.  The up2date and yum were
working well before this change.  After the change, they don't work any
more.  I can launch up2date from KDE, but it just hangs there.  IF I run
yum, is shows, e.g.:

# yum list mysql
Gathering header information file(s) from server(s)
Server: Fedora Core 1 - i386 - Base

then, just hangs there.  The "normal system"'s hostname and ip address
were used by a rh7.3 system.  Now, I took that down and put changed the
new fc1 from "test" to "normal".  Did I miss anything?  Should I do
anything to let up2date and yum work normally?

Thanks!

Hongwei Li