While BIOS (basic input output system) does live on motherboard and needs nothing to boot it does need to satisfy certain conditions before allowing you to access it.
It processes in the way listed below the order of operations first of which is (POST) see explanation and order below, in many cases failing at g) BIOS may freeze before reaching i) the first point at which a user interface is provided allowing access to both keyboard and screen etc which are user interface devices.

1) POST power on self test, the principal duties of the main BIOS during POST are as follows:
a) verify CPU registers
b) verify the integrity of the BIOS code itself
c) verify basic components like DMA, timer, interrupt controller
d) find, size, and verify system main memory
e) initialize BIOS
f) pass control to other specialized extension BIOSes (if installed)
g) identify, organize, and select which devices are available for booting (IF IT FAILS HERE)
h) discover, initialize, and catalog all system buses and devices
i) provide a user interface for system's configuration (IT MAY NOT REACH HERE)