[newbie] Problems with configuration

[semtets]

Hello !
I'm new to Linux, so problems arise everyday.
Working on Mandralke 7.0, I cannot reach any computer in net after rebooting.
Pings are not passing anywhere.
Then I start linuxconf and as a next step just quit (activating changes, which I
haven't made). Everything starts working. I can reach everybody in the
World. That means that all configuration files are correct, but why they don't
load properly ? What's up? Can somebody help me ?

Gennady