I have a second (old) flat screen monitor connected to the second socket on my ATI Radeon graphics card. It was switched off during the previous unsuccessful installs, so I did not think to disconnect it. However, in a last ditch attempt to get the system to start, I turned it on and, Lo, there on the second monitor was the 'enter details' screen in Windows. Entered details and the system started. No idea why a powered off monitor could cause so much trouble.
Now going to plug all drives in, set up RAID 5 and try again.
Will keep you posted.