Hokay, my New Vegas won't start on my main machine, which has:
-Win7 home prem. 64-bit
-6 Gb RAM
-Nvidia Geforce 9800 GT (latest WHQL drivers)
-Audigy 2 (latest (only?) drivers, non-WHQL)

Launcher works, but when I choose play, it shows two first images and then crashes. Testing it on my wife's laptop (AMD P520, 4 GB, Amd 4250, W7 home prem 64-bit) it seems that the game crashes when it should start playing the main menu mp3 file. And to confirm it, I renamed it and I get to the menu. Then I can watch the intro and menu sounds work but when intro ends and the first level is loaded, I hear beginning of sfx and the game crashes with the same StackHash_0a9e code as before neutralizing the mp3 file.

Soooo....
I've returned the file associations of ogg and mp3 to WMP, uninstalled ffdshow and other codecs that I could find, tried with and withoud ALchemy and I'm at my wit's end.

Batch encoding of all sound files to wav would probably not work. Wrong kind of MPEG decoder installed? How can I circumvent it, moving a correct decoder to the NV folder?

I'm installing Fallout3 now and to see whether or not it suffers from the same problem.

Same problem. What should i do? Wanna play

Well, you can try renaming the data/music/special/Mainmenu.mp3 to mainmenu.wav and see if you can get to the menu. Do you also have an Audigy2 sound card? If not, then we'll have to start comparing installed software

Update regarding Fallout 3: same error, same crash, same issues. So some software conflict seems the reason

Oh, thanks! It's working! U are best man u know it?

So it works for you, you can play the game? Well, good for you, I'm still at the same position, sound will crash the game.

I was happy too early. Now i can see Goodsprings. But game crashes when i come to saloon. Twice.

I found the cure!
Tried all variants that i found in internet. Download strange patches and addons, but game crashed anyway.
The decision was simple - I run falloutNV.exe with windows xp sp3 compatibilty mode and IT'S WORKING PERFECTLY, no any [censored] crash for long hours of playing.

I solved mine too: the reason was that I had tried to install a very old Ahead Nero Burning ROM (version 5.5 which had come with my DVD-RW-drive) and even though Windows flat-out told it would not work I installed it and it installed its audio decoder codecs. As the installation borked I couldn't unregister the filters without regedit. The culprit for me was c:\Prog. Files (X86)\Common files\Ahead\DSFilters\Neaudio.ax. Remove it if you don't need it!