Subject identifies the problem. If I unplug the USB hard drive and the USB scanner, the system boots up normally to Windows 7 x86, and both scanner and drive commence to work properly. Motherboard is flashed with the Rev 0072 BIOS dated 8/8/2012. Because the USB devices work properly when plugged in afterward, this would seem to be a defect in the BIOS. Another BIOS update in the works? Client leaves her computer powered 24/7 as a workaround, but this is not a good idea, especially since the power grid in that town is not too reliable.
Anybody doing BIOSes at Intel need more information?