The PC starts and immediately turns off and then turns on again, what could be the problem?

Question

Computers

When you turn on the computer (pressing the PC start key), it automatically turns off, but after a second it turns on again and works fine. It also works fine on reboot.
I suspect that this may be a malfunction with the power supply and also with the battery.
Since every time you turn it on, an error in the BIOS "CMOS checksum error" pops up, which you can press F1 to continue loading.
The PC is still old Pentium 4.
PS
Replacing the tablet solved the problem.

Answer 1

Change the battery (this should be done anyway).
If the problem persists, you will have to change the "dry" electrolytic condensates ... however, it is doubtful that the latter makes any (economic) sense for such an ancient piece of iron :)

Answer 2

Look at the power supply for swollen capacitors. Same thing on the motherboard.