Not enough info, so here are my Qs:
Is your network card detected? ifconfig should list it.
If not, what, exactly, is it? lspci should list it. (Is it enabled in the BIOS?)
Is the dhcp server enabled on your router? (See its manual).
What happens when you ask the router for a dhcp lease with (as root) dhclient eth0 (or whatever your ethernet interface is listed as by ifconfig) ?
Have you tried a different ethernet cable, &/or a different port on your router?
Does your router recognise that it has your PC plugged into one of its ports? Usually, there's a LED or something.
Welcome to LQ!