I just reinstalled Fallout 3 on my windows 7 64 bit computer and as so many others I suddenly have crash issues on new game.
After searching the internet and trying everything I decided to dig a bit myself:
I started Visual Studio C++ express and attached it to my Fallout 3 process, then I tried to start a new game and waited until it stopped responding.
I paused the execution and the game was currently in some DLL code. The call stack contained viscommpgdec.dll and some other video related DLL, selecting the DLL's reviled that they were part of "Fake Webcam", a program long removed. The program apparently left some libraries in Program Files (x86)\Common Files\??? (Can't remember).
First I ran CCleaner and fixed all registry errors. (Fallout 3 still didn't work)
After removing the left over folder containing the DLL's which Fallout 3 apparently uses to decode videos with, I can CCleaner and fixed all registry errors, containing a lot of missing video codec stuff (no surprise).
Started Fallout 3 again, and everything works!!
The thing is, this wasn’t a direct Fallout 3 or Windows error, some other program registered some old (2007) files for handling video which crashes Fallout 3.
I just had to get this off my chest, might help someone else, there might be a codec cleaner program or something if you are not handy with a debugger.
(Don't try this if you don't know what you are doing or if you are unwilling to loose you working windows installation)
No animals were hurt in the making of this post.