Vista restarts during full scan

[Bob]

Twice I've started Defender and left it to run (about 1.5 hours). When I
return, Vista has restarted and presents me with the login screen.

I find this disturbing.

When I bring up Defender, it says everything is fine and seems to correctly
display the time of the last full scan.

Seems like something is amiss. Thanks if you can enlighten me...

 

[1PW]

Twice I've started Defender and left it to run (about 1.5 hours). When I
return, Vista has restarted and presents me with the login screen.

I find this disturbing.

When I bring up Defender, it says everything is fine and seems to correctly
display the time of the last full scan.

Seems like something is amiss. Thanks if you can enlighten me...

Hello Bob:

The first thing that comes to mind is a catastrophic error from your hard
disk drive (HDD) while Windows Defender is scanning.

1) If you do not have a very recent backup of personal data and documents, I
believe you you should do so without delay.

2) Then read:

<http://windows.microsoft.com/en-us/windows-vista/Check-your-hard-disk-for-errors>

Please update this thread with your progress.