bootrec /scanos Comes Up With 0 Installations, although Repair shows Vista OS

My aunt's old Dell Vista 32 bit tower would no longer boot. It gave no error messages - it would go through all the normal startup screens and when it would hit the black screen just before the Welcome.... it would just stay there. Forever.

I tried all the F8 options - Last Good Config, Safe Mode, Safe Mode With Command Prompt, etc, but nothing would get me to the Welcome screen. The first option off F8 was to Repair the PC. That found the OS and took me to the Repair Options screen. Repair Startup found no problems and System Restore had no Restore Points, so I went to the command prompt.

I navigated to C:\Windows and everything seemed to be in order. Bootrec /fixboot and /fixmbr completed successfully, but when I typed in Bootrec /scanos it came back with 0 installations. Bootrec /rebuildbcd won't work because the first thing it does is a /scanos. A reboot changed nothing - just the black screen with the mouse pointer.

I then ran chkdsk /f which (after several hours) found no problems. Of course I cannot do an sfc /scannow from the Recovery Console.

I then restarted and hit F12 to get me to a diagnostics menu. Even the long test passed.

I really have no problem with a reinstall - we've got the Dell Vista SP1 disk, I'd just like to have some idea of what might be the problem, if only to prevent future occurrences.

The Google shows a lot of results for "scanos detects 0 installations", and they're all about trying some things like you tried, rebuilding the BCD, etc.
Sounds like an interesting problem to play around with, but at some point, how much time to invest in the solution?
Based on your other thread to reinstall Vista, I guess you answered the question!

As to the cause of the problem, was there any new/updated program installed recently which may have clobbered the boot data?

Nah, my aunt doesn't download or install anything. She sends and receives email and plays her beloved Pogo games. That's about it.

Her old Vista tower seems okay now, after the reinstall. I'm just puzzled about what happened - It passed every Dell diagnostic, as well as chkdsk and Windows Startup Repair. By all I saw there was nothing wrong with the computer. It just would never get to the Welcome screen. I did keep the old installation when I reinstalled. It's called Windows.old. I have no idea if there'd be anything in there that could possible help in determining what went wrong.