After changing my settings for Godrays to address an aliasing issue the the volumetric fog causes, Fallout 4 will not luanch. It simply closes the launcher when I select play, and then it opens a new launcher. I have tried reverting my settings via the launcher and via the ini files, but I still get the same problem. I have tried re validating my files via steam, I have tried renaming the launcher, but nothing has helped. I'm hoping someone here knows how to help.

This has happened to me multiple time. Quit Steam by going to Steam>Exit in the Steam client and then restart it. That's what fixes it for me.

I might just be shooting the piss, but after I switched to borderless windowed all my graphical/launch errors were resolved, sorry if that just might be dumb.

my fallout 4 did not launch at the start, I don't know if this will help u but, I checked my anti virus, im using Kaspersky, and some of my steam exe's and fallout were flagged , in the application control settings folder as high risk, I just moved them to trusted and then everything worked sweet as
peace

Thanks everyone. For some reason restarting my PC did the trick, and that might be the same as the steam restart. Anyway, it is fixed, so thank you.