Thanks, absic115!
I pressed Enter in the BIOS menu when having highlighted the "Load Optimized Defaults" but nothing seemed to happen, but when I rebooted I noticed that, for example, the setting "Delay For HDD (secs) had changed from 15 (which was the value I "inherited") to 0, so I guess it must have been reset!
However, Under Integrated Peripheals, I notice that the value after PCH SATA Control Mode is set to [IDE], and I thought that I had SATA drives?