You don't necessarily need the Function (fn) key to turn on wireless...

You need ...

A Wireless device
A driver for it (you will have lost this when installing a new O/S)
Control Panel NETWORK settings

You need to establish a network link to your router.

This will not be possible without the device driver for the wireless card....

Control Panel Network & Internet is your best approach. You can connect & disconnect with a click of the mouse button.

Good luck...

Peccavi
February 2013