How conect one subwofeer 12 - DHD NTX-2004 Car Audio Amplifier

Turn the power amplifiers off first and on last. Your problem will go away.

Generally speaking, sub-woofers are not built into notebook computers, as most sub-woofers would not fit. However, there are generally speakers, and there tend to be problems with the audio drivers in most cases if there is no sound for both speakers and headphones.
Within the notebook, there should only be two speakers. If they're missing, did you buy this used or refurbished? If someone just yanked out the two speakers and carelessly cut or handled the wiring improperly, then this could interrupt the headphone bypass cut-off.
I know you mentioned you'd already verified everything appeared to be working properly, and in some cases updating drivers or uninstalling and re-installing them has a positive result. For the obvious, which I've also forgotten to check sometimes, is whether the output is muted within the volume control and mixer.
In case you hadn't already checked out these, here are a few links you may find useful:http://h10032.www1.hp.com/ctg/Manual/c01613382.pdf
http://h10032.www1.hp.com/ctg/Manual/c01613127.pdf

As always, the more complete the information up front, the better the potential for a solution. I hope this helps!

You can connect speakers in your mobile phone and laptop

Look up your question on youtube. Honestly it will help clear things up a lot. Don't worry about the exact subwoofer your connecting it to. But type in "how to connect orion 600d amp to a 12 subwoofer(s)

the rca conection might be grounded or perhaps damaged, why not replacing the rca thats conected to the sub to the amplifier, i had that problem before and when i replaced the rca(usually its a y-form) it worked perfectly

http://www.bcae1.com/spboxnew2.htm

This site will help you with the enclosure.

I believe what you have now is known as a subwoefer. Toss it.

I assume you have told Windows about you new speakers ???
(Start, Settings, Control Panel, Sounds and Audio Devices = Volume tab, Speaker Settings box, Advanced button ...)

Hello Yodybear
First, have to see if all cables conection are fine, 2) check each speakers, to see if all speakers work. 3) use the upmix to 5.1 or 6.1 and see if work, and of course, if your subwofer has this swith or feature.
good luck