The system unit immediately after pressing the power button turns off after 3 seconds, what could it be?

Question

Iron

Unclear. I am facing this for the first time. And so constantly. The power supply has been tested.

Answer 1

look at the motherboard condors. may be swollen

Answer 2

One of the possible reasons: Overclocking, that is, an unsuccessful overclocking attempt. New frequency/voltage parameters were entered, "Save and Reset" was pressed, after which the machine went into reboot and could no longer boot with the new parameters. The CPU fails the initial self-test procedure and sends an ACPI shutdown signal. Shutdown does not happen instantly, but after a couple of seconds. From this state, it will no longer be possible to enter the BIOS. You will have to do a manual reset: when the power is completely off (from the socket), remove the battery from the motherboard and (for a second) short-circuit the contacts to which it is connected. If the original diagnosis is correct, it will bring our patient back to life.

Answer 3

Or the power supply does not have enough power at all or in one of the channels. Overload causes protection to be enabled.

Answer 4

Overheating is possible - there is no cooler on the processor.
Perhaps the absence or malfunction of some component - memory, video card, keyboard.
In general, there is little information - first, connect a beeper or POST tester and see what it says.

Answer 5

closes somewhere. pull out the iron and see where it stops behaving like that

Answer 6

I met in practice with such behavior in case of problems with power supplies (there was not enough power, the unit degraded over time) and a problematic bar of RAM.

Answer 7

If it doesn’t squeak at the same time, most likely the short circuit protection has worked, it’s short somewhere. Either the processor cooler does not start, the percentage overheats - and the protection worked again, but due to overheating. Gut the system manager, everything is on the table, including memory - if it squeaks, then at least it has reached the state of checking for memory availability.

Answer 8

Yes, it's probably closed. You have a button on the front panel, try removing the panel and pressing the button separately. It was like that for me, the base is metal, there is a button on it right away, the button is pressed through slightly, it is not visible outwardly, but it closes as if pressed - I put a piece of polyethylene under the button between.
Are there any sound signals?

Answer 9

The power button sticks. The BIOS counts 4 seconds of the pressed state and turns off. Disassemble the button and adjust the free play. If it is impossible to fix it, replace it, for example, with a reset button.

Answer 10

If it turned on for 3 seconds, it worked, turned off, after 3 seconds it started up and so cyclically. Then pull all the memory and leave only one die. Check. It was with defective memory.