Find the installation driver CDs for your network driver, if you don't have one then note the manufacturer name & model number of your network driver by going to: Control Panel/System/Hardware/Device Manager and see if there is a yellow question mark on the network adapter, note it & download it from internet from somewhere else & install it.
this is how you install it manually if required: comeback to the same location, click on the question mark item, right click on the sub-item, click "Update Driver" choose "Install from a list or a specific location" radio box, next, browse for the .inf that you just downloaded choose the exact name & model then install it.
hope this helps

Thak you.