PC does not boot; how to search for errors?

My notebook does not boot anymore. I dismantled it and tested the components as far as possible.

At power up, only the fan and drive rotate.

The hard disk works, as does the memory. Electricity is obviously available. The display never shows anything, i. I do not come to the bios.

How would you proceed to find the mistake?

Is something blinking on your notebook? For most, there's a blinkcode that tells you where the problem lies.

Otherwise, do you have a USB stick somewhere in it? Or external monitor is turned off or has no power?

Let him run a longer time and check the temperature of the CPU.

If nothing happens, a defective CPU can't be ruled out.
Heat is not proof, but a strong indication.

It is always an advantage to note down exactly when starting a computer, which LED when to approach and what sounds are heard.

In general, the output of the BIOS on the monitor is the last step.

Again, it is worth the documentation of the ads, ie manufacturer and version of the BIOS. Also the information about motherboard… Often at the bottom of the line on the monitor.

This will help you only conditionally, but you could get more concrete indication of the progress of POST (Power On Self Test).

The hard disk should make audible noises when the head is moved. M.W. This only happens when the CPU has started. This should also address an LED for the drive, if available.