I got problems with my redhat linux 8.0 with my cable modem with dynamic ip protocol plug into netgear router, and from router goes into ethernet card into my linux box, and i can't access to my shell or my friend couldn't log in to my shell. Is anyone know why this could happen ?

1. Check for link lights. Try a different network cable.
2. Do you have an ip address? What is the output of /sbin/ifconfig
3. Do you have a default gateway? What is the output of /sbin/route
4. What can you ping and where can you ping it from? try pinging 127.0.0.1, localhost, your internal ip, your router's internal ip, your external address, your friend, your isp, yahoo.com. What works and what doesn't?
5. What the heck do you mean by shell? Maybe ssh or telnet? Is the daemon for such a service running? Are you sure?
6. Do you have a firewall blocking access to some port? Do you have the appropriate ports forwarded on your router if you need to?

Please try to construct complete, coherent, non run-on sentences in your response. Also attempt to include useful information, as it is very difficult to assess a problem without knowing what it is you are talking about.