In desperation, after seeing a couple of entries in Event Viewer relating to errors on a Sata port, I tried reseating the Sata hard disk cable into another port, but no luck. So then I tried using a different Sata cable, and hey presto! - the problem went away, and my PC hasn't frozen for over two weeks. Bizarre, but all I can guess is that there was some marginal problem with the cable. The moral is that it's often easy to blame software for PC problems, but never forget that anything with a bit of wire inside it can fail too.
|Sata cables can fail, too|