Ok long story short, I've been trying to reinstall FO3 for the last 8 hours. I kept getting them message "Fallout has stopped working". Do the cntl alt del to close scenario over and over. I had installed into C/;Bethesda Software, I noticed that when I tried to install FOSE it said it couldn't find Fallout3.exe. When I went looking for it I found it and more FO3 files had been installed un C:/. So I moved them to my Bethesda Software folder. It started up fine, all the DLC showed up in game about 30 seconds into it. I played for about 30 mins with no problems.

So look to see if you have any game files, the exe's the ini's sitting in C:. There may have been 15-20 files that were there, I didn't make a list so I'm not sure which ones they were. I did a sort on the time and pulled in the ones around the same time as Fallout3.exe.

Hope this helps some of you, I noticed quite a few post with the same issue. I thought I'd let you know what worked for me.