An old computer turns on and immediately turns off after 1 second, what are the reasons?

Question

Computers

There is an old computer that is still needed in work. At first it was like this a couple of times: when you turn on the button, it immediately turns off, but when you press the button again, it starts up and works fine, the next day too. On the third day, it stopped starting from the second and third times, it also turns on and stalls.
I cleaned it from dust, there was not much of it, I replaced the thermal paste (not a thick layer). I pulled out the RAM and the computer turned on and, as it should, beeped many times, but when I put the OP back in, it also did not start. I cleaned the contacts of the OP strips with an eraser, tried to insert one at a time and for everyone in different slots. Then he pulled out and cleaned the contacts of the video card, put it back in and the computer started up. But after standing overnight, the next day the same story. This time it did not help to pull out the video card and the OP, but turning off the cooler on the processor from the motherboard and turning it back on helped. And so every time it seems that turning off various parts helps (op, video card, cooler, hard drive ...)
I don’t understand hardware, but I didn’t find swollen capacitors on the motherboard. There are no spare devices for checking and there is no where to get such an old computer from (hardware of about the level of 2005-2008). And I can not decide what needs to be changed in this case, what exactly is buggy.
What does it look like more? Could this be due to a dead motherboard battery? What can be done?

Answer 1

change the electrolytic capacitors in the computer.
the conder swells at the end of its life. but long before swelling, parasitic resistance begins to grow and the conder begins to perform its functions of smoothing ripples worse.
Try to put another, obviously working, power supply. Conders will be fresher in it.