I 'm using RH 7.2 Genome in the Network Configuration I change therer are two places one for static hostname for my machine and in DNS hostname I don't know what happen when restarting my PC when connecting using dialer I can't browse the Internet also I can't use sendmail .......Server timeout cause I change hostname from </etc/hosts what I have to do to restore my Internet connection .............to restore "localhost.localdomain"

I have faced this problem before. Did you try to cat the file /etc/hosts and change your hostname ? Give a try. I did changed the localhost.domain and i lost my network connections. Try to replace the localhost.localdomain and re-try again. In gnome im sure there is a graphical way to change back the localhost, as how you changed it. Try to change back.
Do post again if that solution doesnt help.

but now I have the connection after I delete primary and 2nd DNS but now I have to change the Hostname from >/etc/hosts ....I guess that primary DNS and 2ndary are assigned after the connection have been established .........