Missing Operating System error solution
Hello there; you are probably rebooting the computer first in the BIOS setup section as usb boot and when the usb is installed on the computer. It is usually the first time that usb is booted and you will get this error if you restarted your computer while the usb is not booted. check it out.
usb cd etc which is inserted in the computer. Will the devices be unplugged and restarted?