A Computer That Won't Start: Working Through It in Order

"It won't start" describes at least six different situations, and the fix for each is different. Working out which one you have takes two minutes and eliminates most of the possibilities.

Answer the questions in order. Stop when you reach your situation.

Question 1: does anything happen at all?

No lights, no fans, no sound.

The machine is not receiving power, or is not switching on.

Check, in order: the wall socket with something else, the cable at both ends, the switch on the back of the power supply, and any extension lead or surge protector.

On a laptop: try with the battery removed and mains only, and with the mains only. A dead battery can prevent starting on some models. Check the charger's indicator light, and try a different charger if you can.

If the power supply is fine and nothing happens, the likely candidates are the power supply itself, the front panel button, or the motherboard.

The front panel button is worth checking on a desktop — it connects to the board by two small pins, and a loose or wrongly-placed connector produces exactly this. See inside the case.

Question 2: fans spin, then it stops after a second or two?

A distinctive symptom with a short list of causes.

The CPU power connector, separate from the main motherboard connector. Missing or partly seated. This is the most common cause in a new or recently opened machine.

A short circuit — most often a motherboard standoff where the board has no mounting hole, shorting it against the case. Invisible while assembled.

A failing power supply that cannot sustain load.

Something metallic loose in the case.

Test by removing everything unnecessary, or by running the board outside the case on its box.

Question 3: it stays on but nothing appears on screen?

The machine may be running perfectly with nothing reaching the display.

Check the monitor is plugged into the graphics card, not the motherboard, if a card is fitted. The motherboard outputs are usually disabled once a card is present, and this is the single most common cause of a "dead" machine that is fine.

Check the monitor: its own power, its input selection, and the cable at both ends.

Listen for beeps or look for diagnostic lights on the motherboard. See motherboard lights on but won't start.

Reseat the memory, firmly, until both clips click. Memory is the most common cause of a no-display startup after the monitor connection itself.

Try one memory module alone, in the slot the manual specifies.

Question 4: it shows the manufacturer logo then stops or restarts?

The firmware is running, so the processor, memory and graphics are working. That eliminates a great deal.

The problem is finding or loading the operating system.

Disconnect all USB devices except keyboard and mouse. External drives and hubs frequently hang the process while the firmware tries to enumerate them.

Check the boot order in firmware — it may be pointing at a device that no longer exists.

Check whether the drive appears in firmware at all. If it does not, the problem is physical: cable, power, or a failed drive. If it does, the problem is the operating system.

Clear firmware settings to default, which resolves a surprising number of cases, particularly after a change or a battery replacement.

Question 5: it starts loading the system then fails?

Hardware is largely fine. The operating system is damaged or something it needs is missing.

Try safe mode. If the machine starts in safe mode, the fault is a driver or a startup program rather than the system itself.

Use the built-in recovery options. Both Windows and macOS have startup repair tools that fix boot configuration problems without touching your files.

System restore or a previous version, if the problem started after a change.

If it started after an update, the recovery options include rolling back.

Do not reinstall yet. Startup repair fixes a large share of these and takes minutes.

Question 6: it starts but something is wrong?

Not a startup problem. See why is my computer slow or the specific symptom.

Before you take it anywhere

Note exactly what happens, including how far it gets and any message or beep pattern. "It won't start" gives a technician nothing; "fans spin, three beeps, no display" gives them the answer.

Try the simplest things twice. Cables genuinely do work loose, and reseating memory fixes more than it should.

If your data matters and the machine will not start, the drive can usually be removed and read elsewhere. Say this to whoever repairs it, so they know the data is the priority. See reusing a drive.

Check the warranty before opening anything.

What not to do

Do not change several things at once. You will not know what mattered.

Do not reinstall the system as a first step. It erases your problem along with your files, and frequently the fault was not the system.

Do not keep power-cycling a machine that is making unusual noises. A clicking drive gets worse each time.

Do not buy replacement parts before testing. Borrowing a component or testing yours elsewhere settles it for nothing.

The quick reference

What happens	Where the problem is
Nothing at all	Power: socket, cable, switch, supply, front button
Fans spin, stops in 1–2 seconds	CPU power connector, short circuit, power supply
Stays on, no display	Monitor connection, memory, graphics
Logo then stops	Boot device, USB devices, firmware settings
Starts loading then fails	Operating system — try safe mode and recovery

The short version

Six questions narrow it to a handful of causes, and the first one takes ten seconds.

Fans that spin then stop mean the CPU power connector or a short circuit — that symptom has a short list.

No display with everything running is usually the monitor plugged into the motherboard instead of the graphics card.

Reaching the manufacturer logo is good news — processor, memory and graphics are working.

And note exactly what happens before asking anyone for help. The detail is the diagnosis.

For current Windows procedures and troubleshooting steps, see Microsoft Support.