Have you plugged in the ethernet cable from a router or modem you know is working with another PC?
If so look in the bottom right System tray for the little TV or five bar connection icon, left click to see if a Network is available and try to connect. Next rightclick to run the Troubleshooter.
Click the Start button in bottom left of screen, type Device Manager into search box just above it. Look in Device Manager under Network Adapters. Do you have an installed Ethernet Adapter and is it's driver
To find the drivers
for your PC, search the maker's Support Downloads webpage for drivers. You might also need to seach specs to see what ethernet device is installed to find it's Windows 7 driver. As a last resort you can determine the make/model of the device using Hardware Identification