This was to have been a plea for help in getting my virus scans to work again on my Windows 8 laptop but instead I have posted this to say that I appear to have cured the problem by changing the shut down on my laptop from the default setting (allowing a fast start-up) to a full shutdown, so that the laptop starts with a full boot. I hope this is useful for anyone with similar problems.
The history of the problem (I am sorry it is so long but the story explains why my username is HopelesslyLost) is described below.
For some months I would find that occasionally, although the Norton icon in the system tray showed a green tick, I would not be able to run any scans, either quick or full. Instead of the Scan In Progress window being displayed after requesting a scan, there would be nothing. Until last week I would be able to get the scans to run if I shut down the computer and restarted it.
Last week, I found that scans would not run and a reboot would not restore functionality. Looking at the Performance window I saw that no automatic scans had been performed for several days and a couple of days later the Norton icon showed an orange exclamation mark. On opening Norton I was informed that I needed to run a scan. I clicked the Fix Now button, but got a message that Norton was unable to fix the problem (or something like that).
Researching on the Forum I ran scf /scannow. It told me that some errors had been fixed, but Norton would still not run scans.
I tried running the Norton Power Eraser, but this found no problems and scans would still not run.
I then downloaded the Remove and Reinstall tool. On running this it did something for about 15 minutes showing a progress bar (presumably downloading the zip files that I have subsequently found on the computer). After reaching 100% it started to do perform some other action, but after just a second or so an Unrecoverable Error window was displayed, inviting me to manually uninstall Norton. The link supplied did not take me to those instructions, but merely to the instructions for the Remove and Reinstall Tool. I contacted Norton for a Chat to help me through my problem.
The System Tray icon for Norton had disappeared, but the Desktop Icon was still there. While I waited in the queue I double clicked on this. To my surprise Norton opened, The System tray icon returned and I was able to run scans. When I reached the front of the Chat queue, I told the person at the other end what had happened and left it at that; I would be in touch again if I the problems returned.
I ran both quick and full scans successfully.
The next day after turning the laptop off overnight, again scans would not run. I shut down and restarted again and scans worked.
I had not rebooted since, hibernating my laptop overnight, and all worked fine for a couple of days, except oddly, during one quick scan, Norton opened the Run Scans Help page on the Norton website about half a dozen times during the scan! This has not occurred on subsequent scans.
Then yesterday I had just started a quick scan, the Scan Running window displayed and almost immediately I got an Error 3038, 104 and the scan stopped. I turned the computer off and restarted several times since then and scans would not run. There was no error message, the select scan window just disappeared and was not replaced by the scan running window.
I carried out another scf / scannow and no errors were found. I ran the Norton Power Eraser tool and as before it found no problems.
I checked the hard drive for errors from the drive properties dialog box and no errors were found.
By this time I was thoroughly frustrated and dispirited. I went once more onto the Forum and found this reference https://community.norton.com/t5/Norton-Internet-Security-Norton/3038-104-norton-knowledge-base-info-does-not-look-like-my/m-p/1122360#M257172 .
I turned Fast Startup off, using the information provided in the link in this post, and following a reboot my Norton was working normally again and I can perform scans! I suspect that this will be a permanent cure as one function of another program that had not been running properly for a week or so was also fixed by this full boot. I will report back if the problem is not fixed and I need help.
One particularly worrying feature of this problem was that there was no indication from the icon (no red cross) that there was a problem, only an exclamation mark when there has been no virus scanning whatsoever for 5 days.