while testing/installing stuff over the weekend and playing some music videos in the background the machine spontaneously rebooted. As it came back up the bios reported that the crash was due to "overclocking" errors. Well, the motherboard in the machine is not new in "calendar" terms but it was sealed in it's manufacturers antistatic bag in an un opened box until the moment I built up the machine last week. I have not upgraded the bios or messed with any of the settings so the "overclocking" error, which only shows when some videos are played, seems to be due to the bios not getting it right when interrogating the hardware status. I slowed down the clocks and rebooted and the machine has behaved perfectly all day today.
Time to learn a bit about overclocking, me thinks. I will get it stable and fast, eventually.
Thanks to everyone who has helped me with this issue.
Rans6......