I'm running Windows 7 64bit. Ok weird problem I've never encountered before, but I let my nephew play Fallout 4 on my PC on his user setting, but when I switch back to my user setting the game crashes. I have to go into Steam and run the Validating Steam Files thing and it wil say one of my files had a problem. After I run that, the game starts fine. The other weird thing is after he shuts his game off, I can start the game again on his user setting with no problems. It's only after I switch to my setting that it crashes after the "Please Stand By" animation starts. I thought mabye one of his mods was messing the files up, so tonight I restarted the game, on his user setting, after he had played for a couple hours and it started right up. I've never seen this happen in 20 years or so with any game.