Teste isso:
Abra um terminal.
Execute:
sudo -i
nano /etc/network/interfaces
Adicione as seguintes linhas ao seu adaptador wi-fi.
----------------------------------------------
# The wifi network interface
auto wlan0
iface wlan0 inet static
address 192.168.0.87
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
gateway 192.168.0.1
dns-nameservers 192.168.0.1, 8.8.8.8
wpa-ssid <Your wifi network SSID>
wpa-psk <Your hex encoded wifi WPA password>
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Control + O, salve o arquivo. Control + X, perto de nano.