|All modern PC computers have ATX specification motherboards. They are are always powered in some places, even when the computer is not running, as long as the ATX specification power supply is connected to them and the power supply has live AC power. The power supply is supplying power to the motherboard in that situation even when it's fan is not spinning, |
There is at least one led on the motherboard surface inside the case that indicates the power supply is powering the motherboard even when the computer is not running in that situation - it's there to remind you that you need to remove the AC power to the computer when you are going to be plugging in or unplugging wiring or ram or cards that connect to the motherboard to avoid possibly damaging the motherboard or the ram or the cards.
The led for the network adapter lights up after the power button has been pressed, if there is a good network cable connection between it and whatever it is plugged into.
The led on the mboard and the network adapter led often light up even when the motherboard cannot boot normally, or even when the power supply is defective.
The cpu may get warm after the power button has been pressed when the computer will not boot normally - that is normal.
It's NOT normal for the cpu fan to NOT spin, or for the hard drive to NOT spin, after the power button has been pressed
The fan on the power supply does not spin until slightly after after the power button has been pressed, and that only happens if the mboard has sent a "power good" signal to the power supply through one of the wires in the 20 or 24 pin main connector's wiring to the power supply.
If there is something wrong with the motherboard, or if there is something wrong with the power supply, or if there is a poor connection of the main wiring connector from the power supply to the motherboard socket which isn't likely, the "power good" signal may NOT be sent to the power supply shortly after you press the power button, or it may be sent but the power supply can't respond to it, then the power supply fan does not spin, and the power supply does not fully power up the motherboard.
If you DO have defective capacitors on the mboard, eventually it's common for the motherboard to not "behave" normally while they're failing, e.g. the mboard may restart for no apparent reason, or when you select Shut Down in Windows it may restart instead of shutting off, and eventually the motherboard will not fully boot at all.
The capacitors fail very slowly, although they may explode eventually in the final stages. You usually do not notice any odor - smell - while they're failing.
Power supplies can develop the same bad capacitor problem.
Failing power supplies are common - they often partially work rather than being completely dead - leds may come on, fans and hard drives may spin, yet the power supply fan may not spin and the power supply will not make the motherboard boot fully.
You could try connecting a different known to be good power supply that you have, or someone you know has, that is in a working computer, but if you DO have failing capacitors on the motherboard, that may not be enough to allow your computer to wok normally.
You could also try connecting the power supply in this computer to another working computer to see if it will allow that other computer to work normally.