Onboard or an add in card, the internal workings are the same.
Even without the headset being plugged in, I have seen the spring steel
piece inside the plug be either bent or broken and lock the sound out of any
other port.
It is not likely, but possible.
If it is a brand new machine, call the seller's tech support line and have
them fix it under warranty.

"littleriver" <littleriver@discussions.microsoft.com> wrote in message
news:480B5497-7917-446D-B000-144A8ED80C2D@microsoft.com...[color=blue]
> ports are a group of 6 on the back. Headset was not plugged in.
>
> "Andrew Harris" wrote:
>[color=green]
>> He is being serious. Those sounds cards usually have a ground that turns
>> off
>> the speaker outputs when a device is plugged in to the headphone ports on
>> the front.
>> .
>>
>> Try it.
>>
>> "littleriver" <littleriver@discussions.microsoft.com> wrote in message
>> news:07A05FF3-7847-4E1E-8507-B281DF8FD520@microsoft.com...[color=darkred]
>> > sound cards? Wiring?
>> >
>> > Read the question please!
>> >
>> > There is no sound card. And because it is onboard sound there is no
>> > "wiring"
>> > to configure.
>> >
>> > Dust in the sockets? This is a new PC.
>> >
>> > "Bob" wrote:
>> >
>> >> Unplug the headphones when you want sound to come from your speakers.
>> >>
>> >> "littleriver" <littleriver@discussions.microsoft.com> wrote in message
>> >> news:D1C06003-7E78-4B84-A5F2-B38C9BE4A113@microsoft.com...
>> >> > no sound coming from speakers, but sound coming from headphones.
>> >> >
>> >> > using standard onboard sound on new intel board, new vista HP
>> >> > install.
>> >> >
>> >> > the usual checks show sound is working, no problems in device mgr,
>> >> > no
>> >> > muted
>> >> > sound etc etc.
>> >> >
>> >> > speakers are turned on, plugged in to correct sound port, and work
>> >> > on
>> >> > another system.
>> >> >
>> >> > when i google "no sound vista" I see lots of queries come up on this
>> >> > subject.
>> >> >
>> >> >
>> >>
>> >>
>> >[/color]
>>[/color][/color]