I can't figure out why this error?

Question

Computers

After that, the PC turns off and at the next startup it just gives a start and immediately turns off in the next second. Half an hour ago everything worked stably, I decided to move his HDD to another computer to check something there, then returned it and now this error.
1. Since an error is written there due to a floppy disk, I don’t have it at all.
2. The battery is dead, the option is also proven. (I took this battery and inserted it into another PC, and everything works fine, just like I inserted the working one into the environment of this non-working PC, the error remained the same)

Answer 1

The motherboard has a round flat (pancake-like) battery. Sold in watch shops, for example. And computer stores.
Judging by the antiquity of the computer, this battery could well sit down already.
It is used to keep the clock running when the computer is turned off.
And to save computer settings. The same CMOS.
Replace battery.
Enter BIOS.
Write down the changes (in reality, you can not change anything, but, for example, the clock could be adjusted).
Everything should work.
This battery lasts for several years.

Answer 2

The battery is dead, for example.

Answer 3

CMOS checksum error - default
loaded board. BIOS reset to default settings.