Internet not working. What does 'invalid IP address' mean?

[xesupernatural]

I have two computer and the internet isn't working for one. The modem and everything is plugged in properly, I'm pretty sure, but the internet isn't working. When I try to sign in on msn from that computer the troubleshoot thingy comes up, and it would usually come up with ticks and crosses next to the things that are working and not working, but it only comes up with an exclamation mark next to 'IP address' and says "Your computer appears to have an invalid IP address'.
I've tried turning the computer off and back on and stuff but I can't get it working.
Please help???
I tried what genius54 said and went Control Panel > Network Connections, and the Local Area Connection says 'Network Cable Unplugged'

Does this mean something isn't plugged in right?

[rekha10]

The message "Invalid IP Address" indicates a problem with your computer's network setup. Every computer that uses an Ethernet-type network, such as the Internet, has an Internet Protocol address that lets other computers communicate with it. Without a valid IP address your computer cannot use the network.A variety of reasons can make an IP address invalid, such as address conflicts with other computers and network configuration problems. To fix this issue, contact your ISP . After fixing an ip address, use Ip-details.com to obtain your ip address .