Computer Won't Turn On? Diagnose Which of the 3 Real Categories You're In

“Won't turn on” actually covers three very different failures with different fixes. Mixing them up wastes time. Figure out which one first.

Category A: Completely Dead — No Lights, No Fans, No Sound at All

This is a power-delivery problem before the computer itself ever gets involved.

1. Confirm the wall outlet works — plug something else into it.
2. Check the cable is fully seated at both ends; try a different cable if you have one.
3. If using a power strip/surge protector, make sure it's switched on and try plugging directly into the wall to rule the strip out.
4. Laptops: try the charger on a different laptop if possible, or a different charger on this laptop. Look for the charging LED — no light at all when plugged in points at the adapter or the DC jack, not the laptop's internals.
5. Desktops: check the power supply's physical switch on the back, and if it has a self-test button, use it. A basic PSU tester tells you definitively whether the PSU is producing power, without needing a spare PSU to swap in.

If all of this checks out and there's still nothing — no fan spin, no lights — the power supply (desktop) or charging circuit (laptop) has likely failed.

Category B: Powers On (Fans Spin, Lights On) But No Display

This is the trickiest category because “powers on” gives false reassurance — the machine is alive, but something between boot and video output is broken.

1. Check the monitor first. Confirm it's on, set to the right input source, and try a different cable if you have one.
2. Drain residual power (“flea power”): unplug everything, remove the battery if it's a laptop with a removable one, hold the power button for 20-30 seconds, then reconnect and try again.
3. Listen for beep codes. Most desktop motherboards use a pattern of beeps to indicate what failed before video initializes — the exact meaning varies by BIOS manufacturer, so look up “[your motherboard brand] beep codes.” No beeps at all usually points at the motherboard or PSU rather than RAM/GPU.
4. Reseat RAM. Power off, unplug, remove each stick and reseat it firmly. If you have multiple sticks, try booting with only one at a time in different slots — a single bad stick or bad slot is a very common cause that looks scarier than it is.
5. Reseat the GPU (desktops with a dedicated card): remove and reinstall it, and firmly reconnect its supplementary power connector at both ends. On newer high-wattage GPUs, an unseated connector is a known cause of no-signal issues — inspect it for discoloration while you're in there.
6. Try the integrated graphics output if your CPU has one. If you get a display this way, the dedicated GPU is the suspect.

Category C: Beeps or Error Lights, But No Display

If you got a beep pattern or motherboard diagnostic LEDs (many boards have labeled CPU/RAM/GPU/BOOT indicator lights near the CPU socket), look up exactly what that pattern/light means for your specific motherboard model. This turns a vague “it's broken” into a specific component to reseat, test, or replace.

Quick Reference