Windows only contains basic drivers and for some "special" hardware components you need to download the drivers. Sounds like this is the case for your network drivers.
Normally the drivers are available on the "support" page of the company that made your computer.
So if you have a Dell laptop you would go to the Dell web site, find their support page, and then navigate to the make and model of the computer you have and download the drivers.
This of course may be difficult to do if you cant get to the internet and you may need to get a friend to do it.
Many computers come with a "spare" copy of Windows hidden on the hard disk. Normally if you want to reinstall Windows you can do it from the file hidden on your hard disk.
This is known as a factory reset and it will be exactly as it was when you bought the computer (including all the drivers).
Have a look at the documentation that came with the computer for how to do a factory reset.
Or if you have not got it any more then tell us the make and model of your computer and when can help you.
p.s. In future download the drivers and save them to a memory stick BEFORE doing the reinstall of your operating system.