Does the printer have a memory card/stick slot? this can cause issues, our canon all in one does the same thing if we leave one in it
Lurking in the BIOS there will be a "Boot from" list, in whatever order. To "help" fault finding, this list is often the exact opposite way round to what normal operation would call logical. There is possibly a "boot from USB device" in the list - if its at the top of the list, it will discover that there is something that looks like a bootable device, try to boot from it, find out that it can't and sit there whimpering.
Easiest way out, apart from removing the USB stick, is to disable the "Boot from USB" in BIOS or move it to the back end of the queue.
Changing the CMOS battery is simple and cheap, once it has been located and its means of fixing determined, but it will probably need to be told when it is and where it is before it is brought back into service.