Question BIOS suddenly refuses to boot into OS and force me to load default settings

[kakashidinho]

I have a PC working for 5 years. The motherboard is Gigabyte Z170 D3H. Today suddenly it refused to boot into OS, the screen saying "Failed to boot system, maybe due to incorrect configurations", it suggested I load the optimized default configurations. I did and it booted OK now.

But why? the system has been working fine. I didn't change any config recently. The only thing I changed from the default settings is the memory XMP profile 1 but that was 5 years ago.
Anw, after the BIOS boot fine with default settings, I changed the XMP to profile 1 again and it still work OK. No clue what happened to BIOS.

 

[RayOfDark]

Dead motherboard battery?

 

[kakashidinho]

But if the battery is dead, how can the system still work correctly after I reset the config to default?