Computer Won't Turn On: How to Diagnose and Fix a Dead PC or Mac

Dead Computer — Where Do You Start?

A computer that won't turn on is one of the most alarming tech problems to face — especially when you have work to do or important files on the machine. The good news is that most "dead" computers aren't actually dead. The majority of failures come down to a handful of well-understood causes, and many can be resolved without any parts replacement at all.

This guide walks through a systematic process to diagnose what's happening, from the simplest possible cause to more complex hardware failures.

What Is Your Computer Doing?

The exact symptom when you press power is your most important clue. Each pattern points to a different cause:

Quick Checks First (Before Opening Anything)

1. Check the power cable and outlet. Plug something else into the same outlet to confirm it has power. Try a different power cable if you have one.
2. Check the PSU switch. Desktop power supplies have a physical on/off rocker switch on the back — make sure it's set to On (|).
3. Strip it down. Unplug all USB devices, external drives, monitors (except one), and peripherals. A faulty peripheral can prevent POST.
4. For laptops: Remove the battery (if removable), hold the power button for 30 seconds to discharge capacitors, then reconnect and try again.
5. Check for indicator lights. A laptop with a solid orange or amber power light may be in sleep mode with a stuck resume. Hold power 10 seconds to force shutdown, then power on normally.

Desktop-Specific Steps

Reseat the RAM

RAM that has shifted in its slot is one of the most common causes of a no-POST condition. Open the case, unlatch the RAM modules, remove them, and firmly reseat each one. Try with just one stick first, in the slot specified in your motherboard manual for single-stick operation.

Reseat the GPU

If you have a discrete GPU, remove it and reseat it in the PCIe slot. Also try using the motherboard's onboard video output if present — if the machine boots with onboard video, the GPU has failed.

Test the PSU

A failing power supply is one of the most common hardware failures and is often overlooked. Use a PSU tester (we have one in the shop) or substitute a known-good PSU to rule it out. A dead PSU is a straightforward replacement.

Laptop-Specific Steps

• Check the charger indicator light. If the charging LED doesn't illuminate when plugged in, the charger or the charging port has failed.
• Try a different charger. Borrow the same model charger from someone or purchase a generic. Charger failures are common.
• CMOS reset. On laptops with removable batteries, remove both the main battery and the CMOS coin cell (if accessible), wait 60 seconds, and reassemble. This clears BIOS settings that can prevent boot.

Mac-Specific Steps

SMC Reset (Intel Macs)

The System Management Controller handles power functions. An SMC reset resolves many power-related issues:

• MacBook with T2 chip: Shut down, hold Control+Option+Shift+Power for 10 seconds, release, then press Power normally.
• MacBook without T2: Shut down, hold Shift+Control+Option+Power for 10 seconds, release all simultaneously.
• iMac / Mac mini: Unplug power, wait 15 seconds, reconnect and power on.

Apple Silicon Macs (M1/M2/M3/M4)

Apple Silicon doesn't have a separate SMC. Hold the power button for 10 seconds until the Mac shuts down, then press to restart. If completely unresponsive, connect to power and wait — the battery may simply be depleted.

How We Diagnose and Fix It

When you bring a dead computer to our shop, we run a structured hardware diagnostic. We test the power supply, RAM, storage drive, and motherboard systematically. We check for signs of liquid damage, burnt components, and capacitor failure. For laptops, we test the charging circuit and battery health separately.

Most "dead" computers are repaired same-day. Common repairs: PSU replacement, RAM replacement, GPU reseating, DC jack repair, and CMOS/BIOS reset.