Quote: Originally Posted by arjang
the speaker is set as default. there is audio when i plug my headphone but no audio from my monitor speaker
You don't want the "speaker" set as default output. You want the device your connected to as the default output. In this case, your Monitor. It should be listed in the Playback devices. All devices capable of audio output should be listed. If you want the audio to be played on the monitor speakers, you must select the monitor as the default audio playback device.
The image below shows a sample of Playback devices. It currently indicates Speakers since I have external 5.1 speakers attached. If I want the audio to be played through the TV/Monitor, it needs to be selected as the default playback device.