Before anyone asks: I read nearly every post on crashs in this forum, but not one seemed to describe my problem at all.
I think I'll skip the DXDIAG since I never saw someone actually responding to that, OR that anyone was able to help just because of it.
And somehow nobody gets the same crashes as me (at least nobody that posted his problems here).
Let's get down to it:
What happens? The game freezes. And that would be totally acceptable if it was just CTD, but it isn't. As soon as Fallout 3/New Vegas crashes the whole PC simply freezes. Sometimes the screen simply turns black (and yes, all the plugs are fine) and the PC stops responding. If I listen to music while playing I hear the music for about 5 seconds, but then everything goes bust.
Only solution is a hard reset (and even that doesn't always respond!).
I get a ton of AppCrash reports, and judging by them windows searches for solutions, but clearly, i cant see that. And worse: I cant click the "cancel" button which would simply shut the game down and let me restart it.
At first I thought it would be a general problem with my ATI HD Radeon 5800. It isn't, since EVERY other game runs perfectly, no crash no freeze not even the slightest lag. It's not even a steam error, since CoD runs very fine, Left 4 Dead 1&2 as well and simply every other steam game.
I tried to set the game to only use 2 and even 1 core (Intel i5 processor), turned of anti-aliasing and set water effects and graphics to VERY low (seriously not recognizing a face wasn't that unusual. Sometimes Cass and Sunny looked the same). I updated my card drivers, "down"-dated them since i read somewhere that could help anyone, I re-installed windows 7, reinstalled Vegas several times, clean booted the PC...
I ran fallout 3 in compatibility and windowed mode, didn't try that for New Vegas yet, but I don't suppose it will help much since it didn't for Fallout 3.
If anyone needs the appcrash file or just the text, ask away, and if anyone, against all odds wants to see and read the DXDIAG I'll see what I can do.
Appreciate any help of any kind.
Thanks in advance.

PS: Oh yeah i tried the fix form NewVegasNexus as well. Doesn't work.

Can't do much in terms of helping, sorry mate, but I'm getting this complete PC crash too. It's happening a lot, but there doesn't seem to be any common causes . . The screen will go black and then standby as though it wasn't getting input, while the pc whirred away and was (power light) on. Only solution I found was holding power button for turn off and then starting again. Only happens with New Vegas, never had this with FO3 (and still don't) or any other game. Have also tried setting affinity to lower no. cores running and using the fallout.ini fix for cores as well . T.T anyone else that can help would be greatly appreciated . Sorry I can't offer any more support than the knowledge your not alone . .

Orca