Hi repeat2400,
Welcome to TSF. I have done some research on fixes for your dilema. Hopefully one of these help you with your problem. Post back and let us know th results. It also wouldn't hurt if you could post your system specs on here.
CPU
RAM
Video Card

"My Game Audio / Sound is Messed Up" (i.e. no sound or timing of sound is off, etc.)
This is usually solved by updating your audio / sound drivers.

1A. Update your your sound card drivers
1B. If not remedied yet, disable 7.1 or 5.1 sound output. Use standard 2.1 audio.
1C. Try using analog instead of optical audio output* (thanks OmniNegro).
1D. Put the game into Window Mode (oddly enough, this solves the problem for some)
If that doesn't work, then the problem below may be what's causing your audio issues.



"My Audio / Sound is STILL Messed Up, How Else Can I Fix It?"
If this is the case, it may be a problem caused by the FFDSHOW codec that many often install from either codec packs or manually to watch videos on their computer. Here are your options:

1. Uninstall the FFDSHOW codec via Add/Remove Programs
OR

1. Load a video so that your FFDShow Audio Codec pops up in the system tray
2. Right click the system tray icon "ffdshow audio decoder" (NOT "ffdshow video decoder") and then select "ffdshow Audio Decoder"
3. Select "DirectShow Control" in the list and then click the "edit" button next to the "Don't use ffdshow in:" option
4. Click the "Add" button and select the Fallout EXE for 32 bit or 64 bit version(s) installed


"My Sound Still Isn't Playing! What Else Should I Try?"
This was a suggestion by one of our users. Thanks Andres!

1. Load the game and pause it (hit the Escape / Esc Button)
2. Hit ALT + TAB and open the Task Manager (CTRL + ALT + DEL)
3. Under the Processes tab, Right click the Falloutnv.exe -> Set Priority -> HIGH


"Are There Any Other PC Game Fixes Fore Messed Up Sound?"
Fortunately, yes. As suggested by Alex (thanks!) try the following pc game fix--

1. Load the Control Panel and open "Sounds and Audio Devices" -> Click "Advanced" Under Speaker Settings -> Click the "Performance" Tab
2. Set "Sample Rate Conversion Quality" to "Good" (the bar to the very left)
Done. That's all there is to it.



"Maybe It's My Sound Card?"
This was a suggestion by one of our users. Thanks gr0x! It turns out that his sound card did not support DirectX DirectSound Acceleration.

1. Go to Start -> Run -- type in dxdiag and hit OK
2. Click the "Sound" tab and then click "Test DirectSound" and allow all of the tests to complete
3. If you any errors occur, use the slider to turn off Hardware Sound Acceleration by dragging it all the way to the left so it's labeled as "No Acceleration"
Note: Even if you don't have any errors during the test you can try turning off the acceleration to see if it solves your problem. Turn it back on when you are not playing the game any longer.

 

I had the same problem trying to run New Vegas on my laptop, background music but absolutely no sound effects. I tried everything: Removing ffdshow, running it in window mode, updating sound cards, setting priority to High on task manager, updating directx directsound, patches and updates etc.

The thing that worked for me (you'll need F3 installed) was copy and pasting the .bsn files from the original Fallout 3 folder into the New Vegas Folder. I didnt replace any files, I just added those that were not already there. This enabled all sound effects (footsteps, doors, speech, etc) except gunshots.

HOWEVER, there are many mods available that 'improve' and even replace NV Gun Sounds and by installing one of those, you should fix that issue and get a pretty satisfactory result.

Hope that helps at all, it's not a very 'neat' solution and am not sure why adding the extra files to an already complete game worked. But it did, and now it's alot easier to become immersed in the wasteland.