What is currently plugged into the computer?
Turn the computer off and remove any devices except for the keyboard, mouse, and power cord since it's an All-In-One.
When you have everything unplugged, restart and see if the issue continues. This is especially effective if you have a printer with a card reader as the computer may have became confused and is trying to boot to the card reader on the printer (oddly enough I have seen a ton of these take place).