Sounds like you need to reset your ethernet card under linux. Depending on the distribution you use, you need to re-configure your network settings. You can do it at the command line but the changes will be lost once you reboot.
If you want to do it at the command line, just logon as root, then type:
eth0 00.00.00.00 netmask 255.255.255.0
where eth* is the id of your ethernet card and 00.00.00.00 is the internal ip address that you wish to assign to it. I assume that your netmask setting would be like the above?
to check that the settings have taken effect , just type 'ifconfig -a'.
Once you reboot the system these settings will be lost though. You should make your network settings permanent by following your distribution specific instructions.
Does this make sense??