I have a hardware problem. Jack sensor in my laptop is not working. It doesn't detect a plugged jack. In Ubuntu, I used to force audio to play through headphones using this command:
pacmd set-sink-port 0 analog-output-headphones
In Windows 7, I am looking for a registry key to change or any other solution to change the default audio device from "Speakers" to "Headphones". I don't use my laptop's speakers anyway.