1. Type regedit in run.
         To start run press windows key() + r in your keyboard.
2. Navigate to the following location of Registry Editor:
        HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\UsbStor
3. In the right panel change the value data of Start to 4 to disable and 3 to enable

Sometime it might not work unless you logoff and login.
It works in XP,Vista and Windows 7.

Use it on your own risk.

Remember, the power is yours.