137th Gebirg wrote:
It may also be as simple as a CMOS battery issue. I've experienced similar weird things over the years with the computer forgetting the boot device, local time and other oddities. Replacing the battery generally fixes it.
That's good advice. However, the default bios setting on most machines including this Dell laptop are not set so that a usb drive will have first boot priority. If the bios lost its settings it would default to the internal hdd before the usb drive.