I think you are saying that you can not access the bios…it must have a bios if it was booting but perhaps the access to the bios is corrupted? I would take the unit apart (look for tear down videos of similar models or search for some instructions…I had to do that with my obsolete and uncommon laptop and somehow found enough info). You’ll need to locate the CR2032 or similar bios battery holder on the motherboard and replace the battery.