I have tried most of the fixes listed. It seems that after I tried to save the initial files too an external disc this started happening. I have since redirected the files to be saved onto the main HD.
What started happening?
Actually, it was such a massive import of 500 photos that they had not all converted to DNG files and that was the holdup. I thought it was due to my trying to export them to an external drive that threw LR into a tailspin but it was me not allowing enough time for processing...