Sometimes my Optiplex 9010 tried to boot from my WD My Book external hard drive. Is there any way to prevent this. I have my internal hard drive as the first boot item.
You should remove USB boot from BIOS boot option. If your system can’t find the first boot, it will then try boot up from the 2nd, 3rd, 4th option.
Will that cause any other problems - USB keyboard, printer, scanner?