hi, I had the same problem but I fixed it few min ago, after searching 1000 times on such forums and internet but finally done :)
It was the case with the sony vaio smart network functionality (double sided direction icon situated at notification area, or you can found it thru windows mobility center). it was not checked up there, when I clicked on WLAN option My wifi switch got up :) Thank God... In case If the option is not showing there (in vaio smart network pop-up), you can uninstall the wifi drivers and then restart the system and check the vaio smart network functionality pop-up it should be there. Again you need to create a profile there too which should have the option checked as "Switch LAN/WLAN profile automatically". Hope this will work....