I have just recently purchased NV Ultimate from Steam. I launch the game and the launcher pops up and I once I apply the graphics settings and click play the launcher closes and the game doesn't launch. I have posted in DXDiag for my pc specs. I have verified cache through steam and 1 file seems to be in a loop not sure which file it is though. Also some have posted to disable sli and have done that as well and run as admin for both the launcher and game exe files and I still get the same issue.

No error messages? Have you tried windows xp sp 3 compatibility mode? You need to post your dxdiag in this thread.

Might also try AV exceptions list for both falloutnv.exe and falloutnvlauncher.exe