I remember having the occasional headache when trying to mount Vista partitions with bootable media, but always had better luck when removing the drive and mounting it as an external to another system.
You should be able to download a Vista repair/recovery disc from..."anywhere", really.
This might be a long shot, but give it a try anyways:
Ctrl+Shift+Esc from the black screen w/ cursor to see if the Task Manager will open. If it does, go to the Processes tab and look for explorer.exe and end it. Return to the Applications tab and "New Task...", "explorer.exe".
If that doesn't work, try the "Last Known Good Configuration..." boot option. Something that was recently installed (driver, program, update...) may have busted the system.