How much money can you possibly charge this guy so he can run one game?
Tell him you tried everything you can find on the web and cant get to work, tell him its possible you might never be able to get it to work and more time on it will just cost him more money, charge him the diag fee and send him on his way.
nail. head. hit.
But, y'know, Im as bloody-minded as the next guy when it comes to not wanting to give up on interesting tech problems 'till they are solved. So I get it.
If it was me, and I was inclined to crack it....
1. get chocolate. it may be a long day
2. memtest 6 passes
3. nuke and pave on a fresh (test, known-good) hdd.
4. load only the game, and the drivers req'd for game (sound, video). Install the game. Update *everything* thats been put on (limited drivers, directx, game, windowz)
5. test. If no crash, you're done.
6. If crash - I havent read the thread, but - what do the game's logs say at this point?
7. Have a look at them then email Microsoft tech support and see what they come back with. They will be up on what the issues are with the game and thats your next recourse to continue troubleshooting it after this point theres nothing else you can do on the PC end.
Personally I would not be doing anything with the existing install though. You could be there forever with no result. To many possible unknowns at play.
But, yeah, if you have to go through all that to make it work (even though it may not at the end) you would want to have had the conversation with the customer at the outset that he will still have to pay if there's still no result. I think thats probably unlikely if you do all the work, but its a discussion ya might want to have
Anyhoo, let us know how you get on, eh?
J