You pressed the power button and nothing happened. Or something happened — a light blinked, a fan spun for half a second, there was a click — and then nothing. Before you price a replacement, know that most computers that "won't turn on" are not dead. They are unplugged, confused about power, or one cheap part has failed.
"Won't turn on" covers three very different situations. Work out which one you have and half the diagnosis is done.
First, sort out which failure you have
- Nothing at all — no lights, no fans, no sound when you press the button. This is a power problem: the wall, the cable, the charger or the power supply.
- Lights and fans, but a black screen — the computer is running; the picture is missing. Usually the display, a cable or a loose memory stick.
- It starts, then dies or restarts in a loop — power is fine; something fails during startup. Usually heat, a stuck update or a failing drive.
Take them in order, cheapest suspect first.
Nothing at all: work from the wall inward
Test the outlet first: plug a lamp or a phone charger into the same socket. Skip the power strip and go straight to the wall — strips fail quietly, and a surge protector that has done its job once may never pass power again. Then check the power cable is seated firmly at both ends; cables work loose during cleaning and desk moves more often than anyone admits.
If it's a desktop
Check the power supply switch on the back of the case — a house move or a curious cat flips those more often than you would think. Swap the power cable for a spare if you have one; it is the same lead most monitors use. Still nothing — or a single click when you press the button, or a faint burnt smell — points at the power supply unit itself. The PSU is the part that fails most often in desktops, and one of the cheaper ones to replace.
If it's a laptop
The LEDs are trying to tell you something. Most laptops have a small charging light near the power port: if it stays dark with the charger plugged in, the fault is the charger, the port or the outlet — not the laptop. Many charger bricks have a light of their own; if that is off, the charger is dead. Borrow a matching charger if you can, because chargers die far more often than laptops do. Wiggle the plug gently in its port — a flickering charging light means a loose jack, which is a repairable part, not a dead machine.
The 20-second reset that fixes more than it should
Unplug the power cable and, if the battery is removable, take it out. Hold the power button down for a full 20 to 30 seconds. This drains the leftover charge sitting in the power circuitry and forces it to reset — exactly what a machine needs after a storm, a surge or a bad shutdown. Reconnect the power, leaving a removed battery out for the first attempt, and try again. It looks like superstition; it revives a surprising number of "dead" computers.
Fans spin but the screen stays black
The computer is on; the picture is missing. Prove which side is at fault before blaming either. On a desktop, check the monitor has power and is on the right input — HDMI 1 versus HDMI 2 has wasted many afternoons — then swap the video cable or try a different port. Plugging the monitor into a laptop, or the desktop into a TV, settles the argument in one move.
On a laptop, shine a flashlight at the screen at an angle. If you can faintly see your desktop, the backlight has died, and the machine — and your files — are fine.
If the display checks out, reseat the memory. Power off, unplug, open the case or the laptop's access panel, release the clips on each RAM stick, pull it out and push it back until the clips snap. Heat cycles loosen the contacts over time, and a half-seated stick produces exactly this symptom: fans and lights, no picture. With two sticks, boot with one at a time — if the machine starts on one but not the other, you have found a failed stick.
What the beeps mean
A computer that beeps at startup is running its self-test and failing it — useful, because the pattern names the suspect. One short beep is normally the all-clear. A repeating pattern — three beeps, or one long and two short — usually points at the memory or the graphics card. Count the pattern and search it with your computer maker's name. Beeping plus a black screen right after a move is almost always a RAM stick knocked loose in transit.
It starts, then dies or restarts in a loop
Power is fine here; something fails during startup. Overheating is the common cause — blocked vents, a mat of dust, a fan that screams and then cuts out. Clean the vents and try again on a hard surface. If the machine reaches the Windows logo and restarts, Windows usually offers repair options on the third failed attempt, and Startup Repair is safe to run. If the loop began right after an update, work through the recovery steps for a computer that won't start after a Windows update. A rhythmic clicking or grinding from the case is a drive failing: stop restarting it and read the warning signs of a failing hard drive. And if you catch a flash of blue with white text before each restart, the blue screen guide will decode it.
When it's the motherboard — and when to stop
If a desktop shows no life on a known-good outlet with a known-good cable and power supply, or a laptop stays dark with a working charger after the 20-second reset, the motherboard moves to the top of the list. Other tells: no beeps where there used to be beeps, a burnt smell, a machine that died the night of a thunderstorm. This is where the economics change. A power supply or a charger is a cheap fix; a motherboard is often the most expensive part in the machine, and on an older laptop the repair can cost more than the computer is worth — the computer repair cost guide lays out where that line sits. It is also the point to stop pressing the button: repeatedly powering a shorted board can take healthy parts down with it.
Your files are waiting, safely
In almost all of these failures your files are intact on the drive, which neither knows nor cares that the power supply died. Even a completely dead machine usually gives up its files easily once it is opened up. Do not mourn the photos yet. And once the machine is running again, treat the scare as your prompt to set up a real backup — the next failure might be the drive itself.
If it stays dark after all this
A computer with no power is the one problem remote support cannot touch — someone needs hands on the machine. That is what Koadi Technology is for. Post the problem free, in plain words, with what you have already tried; vetted, identity-verified technicians pick it up, and you either set a fixed price or take bids. Payment sits in escrow until you approve the fix, and every technician is rated publicly. If the machine powers on but misbehaves, remote help is available in every US state, evenings and weekends included; for the truly dark ones, on-site visits come through local vetted technicians.