am going through the exact same thing. I recently went through
anUbuntu upate and a later version of the kernel was loaded and this
went into my grub startup list as the default. I began to
see "Network Disconnected" for the first time. I restarted to
booted with the earlier kernel that was still in the startup list
and the network connected fine. I am using a new Toshiba Satelite
laptop. P.S., I am still having no luck with my Atheros wireless
card that is built in.

If there was a kernel update, it changes things. Hardware is detected by the
kernel and sometimes drivers are compiled for the specific kernel. The kind of
situation that you describe suggests that this is the case here.

As for the Atheros card, try installing ndiswrapper and ndisgtk from the
repositories. You will then have a graphical installer for ndiswrapper in your
menu. You will need your Windows wireless driver disk. Look for the inf file on
that disk and Ubuntu will use that driver.