@ArrBianca usually that means the internal battery that maintains configuration state went dead (the little CR2032 coin cell in desktops... not sure what laptops use)
You get "checksum invalid" because the memory holding that configuration resets to... whatever its uninitialised values are, which are basically junk values.
@SomeEgrets a bit of an issue then, when the computer in question is a laptop with a non-user removable battery, and no separate battery for that purpose
@ArrBianca I definitely don't know how they handle it on more modern laptops. Especially hermetically sealed ones like Apple, so I'm afraid I can't be of much use there :(
@ArrBianca ah yes, that would do it as well!
(I didn't know it was newwwww!)