Your Wifi chipset probably requires a proprietary firmware, which Linux-libre
(hence Trisquel) does not include. We may be able to confirm that if you give
us the output of that command (to be executed from a terminal):
$ lspci | grep Network
The recommended solution is to buy a replacing hardware at ThinkPenguin, the
only reseller that guarantees the device will be handled by Linux-libre.
Besides, by using the link I gave, 25% of the profits made on your purchase
will be donated to the Trisquel project.
Unfortunately, it is possible that your laptop does not allow replacing the
Wifi PCI card. Indeed, Dell now practices "treacherous computing". As a
consequence, you had better acquire a USB Wifi dongle.
