Previously You check in terminal

$ lspci | grep BCM

04:00.0 Network controller: Broadcom Corporation BCM4311 802.11b/g WLAN (rev 01)

If yes,continue to process this

1. Remove the BCM driver (standart SAT) in the kernel.

   Go to terminal command:

   $ sudo apt-get remove bcmwl-kernel-source
   

2. Install alternative driver

   $ sudo apt-get install firmware-b43-installer b43-fwcutter
   

3. Restart Computer

   $ sudo reboot
   

Good luck..