Why does the computer turn on only 30 seconds after the start?

Question

Computers

Surely there are people here who, due to certain circumstances, faced a similar problem.
There is a computer, there are no complaints about its work, after launch it works, no crashes, freezes, reboots and other problems of typical users are observed in it, but there is one "BUT" in its launch. After pressing the start button, nothing happens, more precisely, it turns on, the fans spin, current is supplied to the bulbs on the unit, but there are no signs of start-up on the monitor, then after about 30 seconds, what happens is what should happen immediately after pressing it, which did he do those 30 seconds? What could be the problem?
There is also one story that might help. A couple of years ago, I had exactly the same problem. Only in addition to the above problems, one of the RAM slots did not work yet, and the startup time was getting longer every day. I decided to take it to repair, where they told me that the problem is in the motherboard and it needs to be replaced. At that time, there was no money and I decided to postpone this business until the next. months and plus to save up money for newer hardware, but due to circumstances I needed to copy the data from the hard drive and decided to put it back together. and what do you think? It turned on the first time immediately after pressing it, and all the installed memory was on board. After that, he worked for another 2-3 years. And now the problem appeared again. personally, I assume that somewhere something is moving away or a bad contact, but I can’t imagine where exactly.
PS I really don’t want to carry it in for repairs after this incident

Answer 1

Obviously, something in it is slowly initialized, possibly built using conflicting (incompatible) or even faulty components.

Answer 2

I would do this, pull out everything, leave only the percent and the speaker, press the button and wait for the sound signals from the speaker, see how long it takes if everything is ok, put one memory bar at a time and carry out the same experiment and so on. and at the end we get what slows down the initialization

Answer 3

Are there any swollen capacitors on the motherboard? Purely theoretically, the delay may also be due to the need to warm up some components due to their degradation. This is usually related to power and/or capacitors.
Repairs are different for repairs, and in some cases they use professional terms in a conversation: they immediately see that they are not a "teapot" in front of them, and they conduct an honest dialogue. The same thing works with technical support - I usually start a dialogue with the words: "I have nothing to ping ".