I have been battling this since FO3 and now with FONV. I've tried all the fixes that apply to my system and nothing prevented this bug. For reference here is what I'm running...

XP Pro 32 bit SP2
Athalon II X3 425
Nvidia Palit 9600 GSO 384 mb ram
1 Gig of ram
Nvidia 260.89 video drivers (haven't tried the .99 yet)

Not cutting edge, but more than enough to run FONV in high quality, 4x aa, and 8x af since I'm still using a 19 in CRT monitor at 1024 X 768. I average around 60 fps inside and out, and it only really drops when loading new cells.

Anyway In the Nvidia control panel I tried setting Threaded Optimization to off, it was set to auto by default. Since making that adjustment I have not had any black screen crashes that require a system restart, and previously I was lucky to play for 15 minutes before it crashed.

So if you have the same issues give it a try, might help. I'll update with new information if the black screen bug comes back.

HA , you have the same problem i had , your graphics card isnt powerfull enough to run the game , I have a GeForce GT220 1GB but after 15 minutes the game just blackscreens , your best bet is to change your graphics card , or try to adjust the settings on the NVIDIA controll panel to performance rather than quality , turn the power management to maximum, and in the launcher of the game , turn it to windowed and decrease the resolution to as small as it can go :/ , there is a guy on my thread that explained to me that when direct x 11 came out it was more compatible with the newer cards such as the GTX 400 range,
hope it helps it kind of helped me

My card is not the problem. Like I said I get 60 fps average, and the game runs perfectly smooth on the settings listed. Furthermore my black screen crashes every 15 minutes have totally gone away since turning off threaded optimization. A quick google search shows that a lot of people have issues using nvidia's threaded optimization option. I only posted this so others could try to see if it helped them avoid some of their crashes, not to ask for help with my problem, which I don't seem to have anymore.

What does directx 11 have to do with anything, this game uses directx 9...