Black screen on Vista boot

Following an apparently successful recent partial rebuild of my vista system software(On Instructions of a Microsoft adviser) which included stripping out and re-loading all windows updates and Service Packs (This was done because the system refused to load an IE security patch) , I found that the system had unloaded the ATi drivers for my ASUS/ATI AH3650 graphics card.

I tried a new install of these from the original disk - no joy at all. I tried downloading and installing the latest version from the Asus web site again no joy.

In parallel, I also found that Google earth reported that Direct X 9c was missing and it wouldn't start.. I downloaded a fresh copy of Direct X, again no luck.

Any way, after further fiddling with software, including altering the settings on a device called VGA save from "System" to "Automatic" - it was reporting a memory conflict for drivers, I now in the position where I have a black screen in Vista . The system appears, from the sounds it makes, to load. However, duriing start-up the screen goes and remains blank after the system switches to high resolution - I still see the low-res bios system messages.

This only happens in Vista. The system is dual-booted and XP's fine and running all the Ati/Asus graphics drivers without a problem.

Strangely, once I reported to the MS adviser that I was having induced graphic driver problems with the system following the rebuild he stopped responding to queries and passed me onto his supervisor. !

Safe mode halts at crcdisk.sys and won't go any further.

F8 - 640 bx 480 resolution at start-up no joy.

F8 - last good set-up, no joy

Disk repair using original Cd halts at multi-coloured screen with a white mouse cursor.

No joy trying to run Vista reg-edit on XP - compatibility mode ?

I can see and possibly delete the Vista 64 system files from XP. Question is which one to do to force a graphics driver rebuild.

Any ideas.

Nick