Cant access a machine on the network

[KAJE]

hallo there is this machine i set as a domain controller running windows server 2008 that i am unable even to ping from client machines running windows7 proffessional but they can remotely connect to the server and even access the same network. so what might be the problem here and how can i got about it? please assists

[Geek-9pm]

Have you  done this before? Why do you need a domain controller?
Do you have a security problem?
When using Windows 7 on all other machines, a domain controller is not really needed. Unless you just want it.

You have already looked at this?
http://www.windowsreference.com/windows-server-2008/step-by-step-guide-for-windows-server-2008-domain-controller-and-dns-server-setup/

Here is a video: (Ignore the advertisement)
http://www.youtube.com/watch?v=O4PhcnV8gSs

Maybe you need to give some more details.