I have been using Linux Mint 12 for some time and I remember I had faced similar problems back then but that had been fixed by doing some research. However, this time around with the upgrade to 15, I just cannot get it to work.
I have the Asus u56e-BBL5. There are several people who get this problem on this model I can't find the solution. I have looked at this and this . The problem is that I can see all the available wifi networks and when I enter the password for my home network, it just tries to connect for a bit and then I get a notification that 'wireless disconnected'. I don't even get a connection when I do the wired connection.
On trying this:
sudo modprobe -r iwlwifi , I get
FATAL: Module iwlwifi is in use.. Nothing has worked as of now. This is definitely not a hardware problem because everything works fine on my Mint 12 setup on the same machine.