Many thanks for the reply.
Yes, Aperture did lock up every time I tried to run it. Nothing to do with the video. I tried all of the repair systems including using Time Machine to go back a day or so before the effect was noticed. Each time it would start normally and then after around 15 seconds the deadly spinning disc would appear and then nothing.
The only thing that I was able to do was click onto the surrounding frame and move the entire aperture screen out of the way. I actually did this by accident and when I did I noticed that hiding behind this frame was something that normally appears whenever I launch Safari. A frame with the message saying that the Community Tool bar is not supported by this version of Safari. This has a 'close ' box and that is my normal reaction. because when that is on the screen nothing will work until I kill it.
How this has become a feature of starting up Aperture I cannot imagine, but having just tried opening Aperture again I can confirm that it happened again. I now know to uncover the mystery box and close it, then all works fine. Exactly the same thing happens if I connect a camera. Aperture starts and then locks up until I close the offending box. If I had not looked behind the Aperture screen the mystery would have remained. Obviously there is an explanation, but I am lost!