If that doesn't work, click 'options' and set your resolution to your desktop res, or try windowed mode. IF CRASHING WHEN CLICKING 'PLAY' in the fallout launcher, update Games for Windows Live (click). * Causes fallout 3 crashes: teamspeak 'overwolf', ASUS xonar 'gx' & GamerOSD. * Dual monitors? Either disable 2nd monitor (Windows key + P) or set same res on both. It will validate your game, detect your graphics card and create a fallout.ini.
Start Fallout, click Play, push the escape key and Quit.