Computer Won’t Turn On: No Power, No Lights, No Fans

First, split the two very different faults. Nothing at all — no light, no fan, no sound — is a power delivery problem. Fans spin, no display is a POST problem. They share almost no steps.

Nothing happens at all (desktop)

1. The wall. Try another socket, and another device in the same socket. A dead extension lead or a switched-off socket accounts for a genuinely surprising share of these.
2. The cable. Swap the kettle lead. Test it on a kettle to be sure.
3. The supply switch. Rear-mounted rocker switch on the supply itself — check it is on, and set to your mains voltage if it has a selector.
4. The power button. On the board there is a front-panel header labelled PWR_SW. Unplug it and briefly bridge the two pins with a screwdriver. If the machine starts, the case button or its cable is the fault.
5. Reseat the 24-pin and 8-pin connectors. They click. Partial insertion gives exactly this symptom.
6. The paperclip test on the supply: unplug everything from the board, bridge the green wire to any black wire on the 24-pin, switch on. Fan spins means the supply is probably alive; silence means it is dead. Do this only if you are comfortable doing it.

If all of that passes, the fault is the supply or the board. A spare supply is the fastest way to tell which.

Nothing happens at all (laptop)

1. Charger and port. Check the charger brick's light, try another socket, and try a different USB-C port if it has one.
2. Hard reset. Disconnect the charger, hold the power button for 30 seconds, reconnect, then press power.
3. Battery. If the battery is removable, run it on mains only, then on battery only.
4. Charging light off entirely usually means the charger or the charge port — not the battery.

Fans spin but there is no display

1. Listen for beeps. One short beep is normal POST. Repeating patterns are a memory or graphics code — look up your board's beep table.
2. Monitor input. Confirm you are on the correct source and that the monitor is plugged into the graphics card, not the motherboard.
3. Reseat the memory. Remove every module, then fit one at a time in the slot nearest the CPU. A machine that boots with one stick and not two has a dead stick or a dead slot.
4. Clear CMOS. Unplug, remove the coin cell for thirty seconds, refit.
5. Reseat the graphics card and check any PCIe power leads click home.
6. Disconnect everything non-essential — drives, USB devices, front-panel headers — and try to POST bare.

After a power cut or surge

If the machine died during a storm, suspect the supply first, and do not keep powering it on. A supply that has taken a surge can pass damage down the line. Test with a known-good supply before connecting your drives back.