After the exiting time I had last night with the computer, I finally decided to switch off and go to bed.
This morning, I switched the machine on, and miracle of miracles, it fired up correctly on the FIRST attempt. It has not done that for over a month !!
I then restarted it (yes....I like living dangerously!) and it again fired up correctly.
A few minutes later, I got a notification (via Windows updates) that there are 9 new updates available.
I deselected the .NET Framework updates, and started the process of downloading/installing the Vista updates.
This process got stuck during restart on "Configuring Updates Stage 3-3....Please do not turn off your computer"
After 20 minutes of waiting and nothing happening, I had no option but to force a shut-down with the Power button. On restart, it started fine and to my amazement, all the Vista updates I had selected, had been successfully installed. I am not going to try the .NET Framework updates.....I don't want to push my luck too much at the moment!!
I want to thank you for your patience and kindness in trying to help me. I will, of course, carry out your suggestion later today.
However, I can't help feeling that my Desktop is probably on its last legs!!
Thank you again