I remember seeing people with Realtek sound chips having trouble with Skyrim. Take a look at http://www.gamesas.com/topic/1352866-realtek-low-sound-fix/. Towards the bottom of the page, it's being mentioned that enabling loudness equalization makes things better.
It's also being mentioned on http://www.gamesas.com/topic/1354554-guys-please-i-need-help/, along with the following, which I would read very carefully, if I was you:
I suspect you have very low sound in-game, rather than no sound. I'd like to test that theory really quickly: can you go to your Sounds control panel, right click on whatever audio device you're using with Skyrim, and select "Properties?" Then go to the Enhancements tab and scroll down the list until you find something called "Loudness Equalization." Toggle it on, click Apply and then OK, and then try to run Skyrim.
If I'm right, the sound should become audible again. The trouble is Skyrim derps out hardcoe with anything other than a 5.1 sound set-up: end result is the game seeming to be muted (or in my case, I could only hear about every third word of dialogue, if that). Loudness Equalization is a bandaid fix, though--just toggle it on to test and see if your sound levels are fixed.
I'm not familiar with Creative cards, which I assume is what you have from what I can sort of your dxdiag. This solution to get Skyrim audible again is for Realtek onboard sound, but it may help you sort things out. Basically you'll have to set whatever audio equipment you have to 5.1, even if it's only stereo, for Skyrim to be audible properly.
And finally, whether you have it installed or not, head to Microsoft, download http://www.microsoft.com/download/en/details.aspx?id=8109 and install it. It's always good to be on the safe side, when things come at this point.