IY;
This isn't going to make a whole ton of sense, but it's your problem so we've got to get to the root of it. There is
something in your TCP/IP stack (it's like a stream of software that gets the data from your ethernet card to the operating system and proccesses it) that is not allowing DHCP to negotiate properly. In other words either your ethernet cards can't ask for an IP address, aren't asking correctly, or can't hear the response. Could be some firewall software went in and screwed with things automatically, could be something else entirely.
The next step is to see your TCP/IP settings. I need you to get screenshots of them.
Get to your ethernet card status that looks like this (sans the pink coloring):
Click properties. You'll see this:
Click the TCP/IPv4 item, then properties. You'll see this:
Take screenshots of both tabs, then go back to the general tab and click Advanced. You'll see this:
Take screenshots of each tab.