Open a cmd window and execute command "netsh interface set interface wireless disabled ( or enabled )", Windows 7 would respond message "System cannot find the file specified" but did not tell which file was missing. Any suggestion about how to fix the problem will be much appreciated.

use "netsh interface show interface" to get the interface name of your wireless connection then try "netsh interface set interface name="Wireless Network Connection" admin=DISABLED" where name is your name you got from show interface for detailed syntax see http://technet.microsoft.com/en-us/library/cc770948(WS.10).aspx