Error - unknown filesystem grub rescue - can't boot from any other media whatsoever
You presumably have the BIOS set to "quick boot", which skips the POST and possibly doesn't show information on keys to press to get to the BIOS menus.
According to the Lenovo manual (page 39, marked "35"), you can get the boot menu by mashing F12 when it powers on. From there, you should be able to select a device to boot off of.