When you turn on the computer, nothing happens. What could be?

Question

motherboards

When you press the start button, the computer starts up, but nothing else happens. The monitor is always black. Mouse and keyboard don't work. There is one more oddity, if you de-energize the system unit and re-power it, then it turns on at startup, after 3 seconds it turns off and turns on again, and then everything is the same. Thanks in advance)

Answer 1

Is the fan in the power supply spinning? If not, then try disconnecting the PSU from the motherboard, and connect the black to green wires on the connector. If it spins, then there are problems with the motherboard, if not, then with the PSU itself.
PS. Well, the option with overload and short circuit must be checked - unhook all devices from the connectors, leave only the motherboard.
ZYY. And another option is that the power button itself does not work. Disconnect it from the motherboard, and close the connector contacts with a screwdriver.

Answer 2

This can happen if the memory bar has moved a little. Especially if before that they opened the system unit.
In this case, I take out the memory modules, wipe the connectors and clean the slots. Then I return the memory to its place. It is necessary that the latches on the slots fix the modules well, but without fanaticism, so that the mat. Do not damage the board or memory.
Maybe, by the way, are there any indicators on the motherboard that indicate a problem, or is there a sensor with POST error codes?