When I play a video I have no sound. - HP Compaq 6730b Notebook PC

Does it happen only when you play Video files or is it same in the case of Audio files... considering both the options: In case if you can't here any audio [while playing audio and video files] go to control panel--sound,speech and audio devices and audio devices--sounds and audio devices...make sure mute is unchecked and the device volume is not minimum.OR download the audio drivers from herehttp://h20000.www2.hp.com/bizsupport/TechSupport/DriverDownload.jsp?prodNameId=3687780〈=en&cc=us&taskId=135&prodClassId=-1&prodTypeId=321957&prodSeriesId=3687777
by selecting language and Operating system.
second option where you can't hear the audio while playing the video files only...this is the case of either a missing codec or some option in the Video player.I suggest you to use VLC player http://www.videolan.org/vlc/ for playing a lot of formats. or either tell me which player are you using...I could give you a codec link or sort out any option that is preventing you from hearing any audio.