No video on boot-up in Vista 64

I'm going to try this again because I think I now have a much clearer
idea of the underlying problem.

Situation: quad-boot Intel CoreDuo machine with 4 GB of memory and an
ATI AIW X1900 Radeon—the video disappears immediately
after the green startup wait indicator in Vista 64. All other systems
working perfectly.

What I have discovered:
1. I can access the system in safe mode
2. when I do so, there is no video-controller device listed in device
manager
3. a hardware scan in safe mode does not recognize the video board
4. attempting to reinstall the ATI driver fails because the
installation does not find the board
5. I cannot access the system in low-resolution mode
6. I cannot get boot logging to work

I now believe that this problem may have resulted from some nasty
interaction between Windows Speech-Recognition and ATI Catalyst the
last time I used the system. All kinds of strange things began to
occur with Catalyst. I would guess that Windows Speech-Recognition
somehow interacts with Catalyst, probably because of the notorious ATI
External Event Utility. If I ever get this working, I'm going to
permanently disable that largely useless and known-to-be-buggy
utility.

Is there anything I can do to save the system or will I have to nuke
it and start over?