Windows Defender will not complete scan on Windows Vista build 560

[Guest]

Windows defender is reporting that I have not scanned my computer for 17
days. It then says that "We recommend that you schedule Windows Defender to
scan your computer each day" Which at the bottom of the Windows Defender home
tab I can see it is sceduled to scan everyday at 2:00 AM. There is a Scan
Now button on that screen. When this button is pressed Defender starts a
scan and runs forever. Never finishes. I have left the machine up over the
weekend and the same scan will be running until I reboot or tell the scan to
stop and also exit defender from the task bar. How can I fix this. Thanks

 

[Guest]

Forgot to add system info from Defender:

Windows Defender Version: 1.1.1505.0
Engine Version: 1.1.1609.0
Definition Version: 1.14.1736.7

 

[Bill Sanderson]

Are you set to do full scans or quick scans?

I'd recommend setting it to do quick scans, but that's kind of abdicating
the question about what's really wrong.

I can think of several possibilities--in the past, malware has set
permissions on some objects such that beta versions got "stuck"
scanning--particularly in the registry. I think observation of where it is
hanging up is about all we have to go by. I suppose there could be disk
problems that might slow the scan down--scandisk should tell about that--but
it seems an outside chance. Defender scans inside archives, including .ISO
files. If your system has a large number of such files with lots of files
in them, this would lengthen the scan--but would it really be that long?
You can set options not to scan inside archives.