my audio is gone now

Are you using HDMI audio through your monitor? If so you will probably need to reinstall the nvidia drivers (do a custom install and select 'clean install'.)
The following will probably have to be done regardless of HD Audio (hdmi) or regular audio; the difference will be in selecting what type audio will be default.
Go to control panel>sound. Make sure the the icon "Speakers" has a green n white check mark and is labeled Default Device; if it doesn't have this check mark, right-click and make it the default device. Then go to the tab at the top "Sounds".
Make sure your speakers are on or headphones plugged in and on, in the Program Events window click something with a speaker next to it then click test and see if you get sound.
Let us know how it turns out.
Oh ya, almost forgot. Make certain you didn't inadvertantly unplug your speakers from the back of the PC when you were moving it around and installing the new card; has happened to this very impatient old guy a couple times. Kinda embarrassing after all the bad names I called my computer - to discover something so simple.

Reinstall all of the Audio drivers as well as reinstall the Nvidia drivers for the new card.
It is not uncommon for drivers to get lost or erased when new equipment is installed. (if that makes you feel any better)
Let us know.
{I am calling it a night very soon, and probably won't get back on until late tomorrow or Sunday, but I will get back to you}

How did it go? Get your sound back?

Have you looked in Device Manger to see what sound controllers are there?
Also, can you please list the mother board model, make, chipset etc. and the exact model and make or your powersupply.
We'll give this another try.

O.k., thanks. Please don't take offense at what I have to say, but IMHO Compaq pc's aren't very good. My experience with them is from my family; my son had 3 of them starting in the mid-1990's. One was a $1400 gaming machine I bought him for Christmas. All of them failed, the expensive one somewhat catastrophically. I built a PC for him for the Christmas of, I believe, 2003. The case was a bit battered, but it was still working this past October when I sold it at a yard sale.
That being said, did you hunt down drivers for your Audio at Realtek and install them? If you did, and the RealTek High Definition Audio didn't show up in the Device Manager>Sound, video and game controllers window (this is different then Control Panel>Sound), then that part of the mother board has probably been damaged.
And it was probably NOTHING that you did!!
You could try a complete re-install of Windows because it could be a corrupted file therein, but I wouldn't hold much hope.
Since you ordered a sound card, that may be the only solution: if it works then HALLELUJAH!
Moving forward I would start saving for other parts to build a new machine. Another 4 GB of DDR3 1333, new mobo and processor (either brand), and a bigger hard drive. Spread the purchases over time and it won't be such a shock to your bank account.

UPdate/Edit: Skip to the bottom, and if what I mention down there doesn't apply, come back and read the first part just below this paragraph: It dawned on me about 1/2hr ago that if the audio chip was damaged it probably wouldn't have shown up in Device Manager as working!

You have had the right idea, to upgrade that PC into one that will run games, but my limited research of the mobo tells me it wasn't the strongest M2N board made. The computer isn't crap, the HP's just aren't generally built "strong" enough for intensive gaming etc. IMHO.
Regarding the Device Manager: GREAT! the 'parts' show up in there and are supposedly working. The Nvidia stuff is for your HDMI audio, so I don't think we need to be concerned with this.
Have you gone into the BIOS and made certain that the on-board Realtek audio is selected? You are going to have to go in there when you get the new sound card - to disable on-board sound - so if you haven't tried that, give it a shot.
Re. a windows reinstall; yes, everything will be wiped out with a clean install of Windows; but make this the Truly last resort option because of all the reinstalls and saving of information you have to do.

Lastly, the question of parts failure. Unfortunately, sometimes things just wear out. There might have been a power fluctuation, a solder joint may have finally given up and un-soldered(in the chip or mobo itself), static electricity may have done it in: The list could go on but you get the point.
BTW, you have probably already done this but I went on ASUS website and cannot find this motherboard, even though I have seen pictures of it. Pegatron was a susidiary of ASUS until 2010, and susidiaries of Pegatron (since 2010) include ASRock . I could not find any information on their website re. the mobo, but it appears identical to the ASUS board.
That PC isn't ancient and you are on the right path to keep it going for awhile but at some point it will or has become more expensive, and frustrating, to keep running then it would be to build one, or take your psu and graphics card and buy a $400 pc at, say Wal-Mart, and install your upgraded components in the new inexpensive pc.
BTW, I unselected the solution so that others may jump in with more or different information. Thanks for selecting my answer and I would be pleased if you did so again, but let's see if we can fix the problem first.

Forgive me if you have already tried this.
Go to device manager>sound etc. controllers. Right click on the RealTEk Audio and uninstall it. Do Not restart yet.
Go to Programs and Features (Control Panel) and uninstall/remove everything re. audio by RealTek: Careful here, you have RealTek LAN for your internet and you do NOT want to uninstall those.
Re-boot and on reboot, go into the BIOS (press Delete or which ever key will get you into setup/bios, at the start of the power up). Find the audio selection and select on-board audio.
After re-boot, reinstall your realtek audio drivers. You probably will need to reboot again.
Then make sure RT shows up in device manager. It should.
Go to Control Panel > Sound and see if the RT shows up under Speakers. If it finally does, select as default.
If you have already done all of this, perhaps numerous times, call me a bad name and swear for wasting more time, then read the stuff at the top.
Have a safe trip, looking forward to some sort of reply (good or bad) on Tuesday.

Try it again, and follow the steps I gave you. You have to manually install the drivers; do NOT let Windows do it automatically. You may have to down load the drivers from the Mother Board manufacturer or from RealTek and save them to the desk top (where you can find them).

roger that. good luck.

Neither board will work with your system. The ASUS is an ATX size, and your case takes a microATX. The Foxconn is ancient equipment using DDR2 RAM, and if the HP that you linked to is truly your PC, your's uses DDR3.

See what the sound card does. Have you made contact with HP to see if they can help or if they have mobo's?

it should fit, and your RAM will work, and it says it will take an Athlon II so your CPU should fit. It will NOT run Nvidia SLI if sometime in the future you want to run two video cards, but I doubt that the Power Supply in that HP would support two GPU's.
Here's the link direct to Newegg for that board; I don't much like eBay, been burned to many times. I would order direct.
[strike]http://www.newegg.com/Product/Product.aspx?Item=N82E16813128627[/strike]

I'm going to call it quits for awhile (well, at least for tonight), but again, some advise from an elder with a lot of lifetime experience: Call HP or email them and see if they have any other ideas re. the sound. They might have a BIOS update that would take care of it, and install that sound card and see if that works, before you spend $65 on another mobo.