Hi there,
first off, awesome game. Played it for 192 hours so far and, yes I still would play a little more. Would. If it let me.
The thing is that I bought and installed Dead Money via Steam. So far so good, worked peachy until I decided to go to bed and turned the PC off. Next day when I wanted to play some more, the game wouldn't work. First I blamed installed mods (only 3 anyway), the FOMM, tried to disable Dead Money via FOMM, all to no avail. Several hours of digging into why this game wouldnt load past the first Bethesda screen anymore (if it got that far), I found the falloutNV.esm was missing. How on earth would that heappen? No clue, but if that file is missing it should be able to be reinstalled right? Wrong. I installed the game two more times and still the falloutNV.esm won't show up.
How do I fix that?

Quick thought. Maybe anti-virus is the culprit? Make sure it isnt quarantining the file.

Thanks for the input! Unfortunately that's not the case. Nothing has been quarantined since I got FONV.