my laptop is dell inspiron i5 3543 5th generation the command lspci -nn -d 14e4: shows the following result Broadcom Corporation BCM43142 802.11b/g/n [14e4:4365] (rev 01)
i dont know whether its my hardware problem or it is ubuntu
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Go to Network in System Settings Click on to WiFi. Click the Use as Hotspot button. If you are already connected to a wireless network, you will be asked if you want to disconnect from that network.
If it successfully connected then enjoy!! or else it will be your hardware problem.
Search for appropriate drivers for your configuration.