I seem to have resolved it...eventually a window came up to say clips were missing and I reconnected those and my project opens...relief!
I don't think I moved the clips but seems I must have. Still don't know why it asked for a disk though.
I have just tried to open a recently completed project and a message box come up that says 'There is no disk. Please insert a disk into drive E'
I can't get rid of the message and several attempts all result in the same outcome.