Closes when I press play

[crappypoopy17]

When I launch it its fine than when I press play it just closes

[Doggy Friend]

Try setting both launcher and game .exe files to use high performance in Nvidia settings.
If it doesn't work, try removing both .ini files in Documents/MyGames/Fallout3 folder.
If it doesn't work, go back to Nvidia settings and try to set high performance as default option globally, for all applications.
If it doesn't work, try to repeat the step about .ini files again.