|Have you installed all the device drivers for your built in hardware and any other add on hardware.|
In particular have you installed your network Interface Card (NIC) driver?
This driver is required for your network port to work.
Look and check this in device manager as follows:
Start > Right click on My Computer and select properties
On the window that opens
Click on the hardware tab
then click on Device manager
Check if your network interface is listed under Network Adapters
check if there are yellow exclamation marks against any devices
Yellow exclamation mark means a driver is missing.
☺ When everything else fails, read the instructions.