Someone please help! Whenever I play my game, the screen fades to black and I am unable to move. Whilst the screen is black, either feral ghoul sounds or water splashing sounds play. After this, it fades back to normal. Then, a few seconds later, the same thing happens. Then again. Then again. I'd really like to know how to fix this. Thanks!

Do you use any mods?

Try a game cache verify:
1) Open Steam
2) Right click on Fallout: New Vegas
3) Hit Properties
4) Click the "Local Files" tab
5) Click on "Verify Integrity of Game Cache"