dell - Can't enable the proprietary drivers for Broadcom BCM43142 wireless after installing Ubuntu 14.10? Offline package required?

I have installed the new Ubuntu 14.10 on my Dell Inspiron 3521.

I was able to use my wifi in the Boot Live Stage and during the Installation phase by enabling the BroadCom BCM 43142 proprietary drivers.

But after installation I can't enable the proprietary drivers.

I can see the drivers listed there and when I select the option to use them and click Apply, the progress bar starts going ahead but stops in process and the 'Do not use them' option gets reselected.

I have searched some questions here according to which I must connect my laptop with an ethernet cable to get my wifi drivers working.

But I don't have any ethernet cable at present with me. I can only use the wifi on my second laptop.

Is there any other way to get the drivers working or Is there any offline installer like a .deb file for the drivers?

If anyone knows, please help!

I've reinstalled ubuntu thrice but the problem remains same.