Two PCs sit on the desk, both called dead. One shows absolutely nothing when the button is pressed. The other hums with fans and lights but never paints a picture. They share a nickname and almost nothing else — the first is a power problem, the second usually is not. Telling them apart takes two minutes and saves you from replacing the wrong part.
Most wrong repairs start with a wrong first sentence. Completely dead and fans but no display get bundled into one complaint, yet they point at different halves of the machine. The dead one never received or never delivered power. The humming one has power — something after the power stage is stopping it: the picture path, or the self-test that runs before the picture exists. This page is the split itself — how to be sure which family you own, and what each family honestly costs.
A PC wakes up in stages. First the power supply must deliver standby power and then full power when the button asks. Only after that does the board run its self-test — processor, memory, graphics — and only at the end of the test does a picture appear. A totally dead PC fails at stage one: nothing lights, nothing moves. A fans-but-no-display PC passes stage one and fails later. Every check you run should aim at one stage only; that is what makes the diagnosis fast instead of random.
Work the chain in order: the wall socket, the extension board, the supply's own rocker switch, the cable. If the chain is good and the board's small standby light (many boards have one) is still dark, suspicion lands on the power supply itself or, less often, the board's power stage. Be honest about the test limit here: the only certain home test for a supply is a swap with a known-good one. Shops do this in five minutes because they keep a spare on the shelf. Guessing and buying first is how people end up owning a new power supply and a still-dead PC.
When fans spin and stay spinning, stop shopping for power supplies and look at the two remaining suspects. First, the picture path: monitor on the wrong input, a dead cable, or the cable plugged into the motherboard's port while a graphics card is fitted. Second, the self-test: most often the RAM is not being accepted — a stick slightly unseated, oxidised contacts, or a stick that has genuinely failed. That is why the RAM reseat, and then the one-stick minimal boot, are the highest-value moves for this family. A graphics card that has crept out of its slot during a move is the third regular.
Gather witnesses. Keyboard: tap Num Lock or Caps Lock — if its light toggles, the machine is alive and thinking, and your problem is almost certainly just the picture. Ears: a Windows start sound or login chime says the same. Board: look for a standby light and any debug LED stuck on one label. Monitor: if it shows its own menu when you press its buttons, the panel works and the signal is what is missing. Two minutes of witnessing beats an hour of swapping parts, because each witness deletes half the suspect list.
The honest economics: the dead family most often ends at the wall chain (free) or a power supply (a modest, standard part). The fans-but-no-display family most often ends at a reseat or a cable (free) or one RAM stick (also modest). The expensive verdicts — motherboard, processor — exist, but they are the minority, and they are reached by elimination, not by first guess. Anyone who diagnoses a motherboard in the first minute, in either family, is selling you something.
The video shows a non-starting PC being read like this — symptom first, family second, parts last. It is the cheapest habit in repairs.
▶️ Watch Full VideoYes, and this catches many people. A power supply delivers several voltages, and a weak one can manage the easy loads — fans and lights — while failing on another line or collapsing when the processor and graphics card start drawing real power. Fan movement proves electricity arrives; it does not prove the supply is healthy. The swap test with a known-good supply is the honest decider.
Gather witnesses before blaming either. If the keyboard's Num Lock light toggles and you hear Windows start sounds, the PC has booted and only the picture is missing — suspect the monitor input source, the cable, or the cable sitting in the motherboard's video port instead of the graphics card's. If the keyboard is lifeless too, the PC itself is stuck in its self-test and the RAM reseat is the first move.
No. Many modern cases and boards ship without the small speaker that produces beeps, so a healthy machine may also start in silence. Silence alone proves nothing either way. Use the debug LEDs if your board has them, the keyboard lights as a witness, and the minimal-boot test instead of reading meaning into a beep that was never installed.