Ben, Thanks. I'll have a look at the video, sounds useful.
Just for completeness you asked some questions above, so I'll answer them. No, I never have my project files on networked drives (nor on Flash or USB drives), always on the local hard drive of the computer where NVivo is running.
Actually what I had done was – after the crash – copy both the project and the log file (in fact the directory where they both were located) away to another place on the disk. NVivo wouldn't open the project from that new location (error message about corruption etc.), but when I put both project and log file back to where they had been at the time of the crash (recreating the directory) then all worked fine. I assume somewhere in the project or log file there's a record of the actual pathnames in use.