It is ok now. I did this :
1) Command : rfkill list
0: dell-wifi: Wireless LAN
Soft blocked: no
Hard blocked: yes
1: dell-bluetooth: Bluetooth
Soft blocked: yes
Hard blocked: yes
2: phy0: Wireless LAN
Soft blocked: no
Hard blocked: no
2) Command : sudo rfkill unblock all
3) Command : rfkill list
0: dell-wifi: Wireless LAN
Soft blocked: no
Hard blocked: yes
1: dell-bluetooth: Bluetooth
Soft blocked: yes
Hard blocked: yes
2: phy0: Wireless LAN
Soft blocked: no
Hard blocked: no
3) Turn on the hardware switch and it is OK.
4) Command : rfkill list
0: dell-wifi: Wireless LAN
Soft blocked: no
Hard blocked: no
1: dell-bluetooth: Bluetooth
Soft blocked: no
Hard blocked: no
2: phy0: Wireless LAN
Soft blocked: no
Hard blocked: no
3: hci0: Bluetooth
Soft blocked: no
It is ok now. I did this :
1) Command : rfkill list
0: dell-wifi: Wireless LAN
Soft blocked: no
Hard blocked: yes
1: dell-bluetooth: Bluetooth
Soft blocked: yes
Hard blocked: yes
2: phy0: Wireless LAN
Soft blocked: no
Hard blocked: no
2) Command : sudo rfkill unblock all
3) Command : rfkill list
0: dell-wifi: Wireless LAN
Soft blocked: no
Hard blocked: yes
1: dell-bluetooth: Bluetooth
Soft blocked: yes
Hard blocked: yes
2: phy0: Wireless LAN
Soft blocked: no
Hard blocked: no
3) Turn on the hardware switch and it is OK.
4) Command : rfkill list
0: dell-wifi: Wireless LAN
Soft blocked: no
Hard blocked: no
1: dell-bluetooth: Bluetooth
Soft blocked: no
Hard blocked: no
2: phy0: Wireless LAN
Soft blocked: no
Hard blocked: no
3: hci0: Bluetooth
Soft blocked: no
BUT why it doesn't work after the installation ?