follow the below link
Here go to the section b43: No internet access
follow the steps in this section.
Note: b43 fwcutter is a must so without step 1 do not proceed to further steps.
Once done with all 4 steps goto the section switching between drivers:
Herein remove (if existing) drivers. It might happen that some driver will not be there.
for my case: after doing sudo modprobe -r wl
I got error: FATAL: wl not loaded. So not to worry
Then do loading them, by following the commands.
Once you are done please check:
1) sudo rfkill list all
if it shows as below:
0: phy0: Wireless LAN
Soft blocked: no
Hard blocked: yes
Hard blocked yes means there is hardware switch on your computer/laptop which has disabled the wifi.
With this : Hardware swicth blocked can be seen under wireless icon.
Now to turn it on read below:
for my case: dell inspiron 1525, press Fn+Alt+F2 to turn on the wifi.