If you have the same Problem try the following.
right click Fallout new vegas in the steam menu and go to properties.
uncheck the "enable steamcommunity In-Game" and press on ok
after that restart steam and try to run the game again.
That did it for me. I have no idea what is the problem with the in-game community but maybe that will be solved with a new update.
I hope that will do it for you too.