Not this again!.
Half of fallout 3 was ported from the Xbox 360 game version to the Pc.
Because of that people get a a lot of errors and crashing.
It`s down to bad loose coding and the ported source code from one device to another.
The coding is not tight or full optimized for the said device running it.
The result, lot`s of bugs, crashing, failing to start or execute.
If you look that is why it crashes, not just on your system, and no doubt have read of loads of other people having the same problem.
And yes I have played it and it crashed more times than I can count on my fingers to remember!.
So it`s not just you or, I doubt your system.
What it is is laziness.
And the tricks games company`s use to speed the development of a said game by porting it to another device not having to code it from scratch for each device the game is made for to get them up to speed for release date or launch of the game title.
Not having to write clean, structured code for the device it was intended to be used on.
Fallout 3 is the primary example of what happens when taking this route.