network connection lost ubuntu 7.10

Hi I'm a newbie in ubuntu-linux, I installed 7.10 on a brand-new Dell inspiron 1420 with a wired network connection in my university.
First two weeks: everything went fine, with the default Ubuntu settings I had full connection to the local (windows) network and to the internet,
Third week: internet connection lost, but changing the roaming mode to DHCP in every session the internet connection was recovered (but in the next session was lost again).
Fourth week: no internet no local network, the change in the DHCP does not work.
I have no experience neither knowledge in networks, I'm simply a chemist, but some info that I have found in forums suggests it could be something related with ipv6 connection, but sincerely I have no ideal about what ipv is. How can I recover my network connection? (The guy in charge of the network claims he is responsible only for windows machines, and my problems are my fault).