All PCs very occasionaly fail to boot (for some random glitch) and a reboot then behaves as normal.
The message gives a clue 'No bios installed' which if true means the BIOS chip has failed, and not much more can be done.
You have to bite the bullet sooner or later and switch off.
It may as I hope not bother you again and if it does, then you may have to do special things depending on how the error message settles down.
Before you switch off, just check that the system time and date make sense. If they don't then you probably need a new motherboard battery anyway.