PC won't start? No power, no POST, no video - triage in that order

The symptom: you press the power button and nothing happens. Or something happens - fans, lights - but the screen never wakes. Or the machine beeps at you like a smoke alarm. These are three different failures wearing one symptom, and the family you belong to decides everything that follows.

Likely causes, most common first

Family 1 - no power at all: no LEDs, no fans, no sound. Almost always the power path, not the computer: dead wall socket or tripped surge strip, loose IEC cable, PSU rocker switch left off after a move, or a laptop charger that is not actually charging (check the charge LED on the machine, not the brick's light). Family 2 - power but no POST: fans spin, maybe LEDs, but nothing before Windows - no logo, no beep of success. This is hardware talking to you before any operating system loads: memory not detected or failing, CMOS battery flat, a board or CPU fault. Family 3 - POST passes but no video: you hear or see the machine get past self-test and then a black screen. That is usually a graphics driver or display-path problem, and it is the family with the softest fixes.

Diagnosis

Work the families in order, cheapest check first. Family 1: prove the socket with a lamp, reseat both ends of the power cable, flip the PSU switch, bypass the extension strip. On a laptop, unplug, hold power 15 seconds, replug, watch the charge LED. Family 2: listen and look. Beep codes and diagnostic LEDs are the motherboard naming the faulty part before any OS exists - on Dell desktops, for example, two or four beeps mean memory (reseat or swap RAM sticks, one at a time, in the primary slot), five means the CMOS battery, and one, three or seven point at the board, chipset or CPU and mean running the vendor's pre-boot diagnostics rather than guessing. Blinking-amber power LEDs generally mean no-POST; solid-and-alive LEDs with a black screen move you to Family 3. Family 3: force-shutdown by holding the power button about ten seconds, twice or three times, until Windows recovery appears; from Troubleshoot > Advanced options > Startup Settings boot safe mode (F5 for networking) and roll back or update the display driver; test an external monitor to split GPU from panel.

Fix

Family 1 fixes are the cable, the socket, the strip, or a replacement charger/PSU. Family 2 fixes are reseating RAM (and cleaning the contacts), replacing a coin-cell CMOS battery, or clearing one stubborn peripheral by booting minimal - one stick of RAM, no drives you can remove, nothing on USB. Family 3 fixes are driver rollback in safe mode, a display-driver clean reinstall, or the external-monitor workaround while you order a panel or cable.

When this fix will not work

If beep codes 1, 3 or 7 (board, chipset, CPU) persist after a pre-boot diagnostic pass, or the machine shows no POST with one known-good RAM stick in each slot in turn, you are no longer troubleshooting - you are quoting a repair. Same if the PSU test or a known-good swap implicates the supply on a machine out of warranty: the part is cheap, the labour and risk are not.

When to escalate

Two things before any repair decision: your files live on the storage device, not on the dead motherboard or PSU - a machine that will not POST can still give up its data via drive removal or a professional service, so say so before anyone formats anything. And run the dead-machine arithmetic on repair vs replace: board-level work on an out-of-warranty machine older than about five years usually loses to replacement, while a reseat, a coin cell, or a cable is free.

Official documentation (checked 16 September 2026): Dell KB 000124349, Understanding beep codes on Dell desktop PCs (codes 1-7 and their fault classes); Dell KB 000132276, Inspiron desktop diagnostic indicators (power-LED states separating no-power from no-POST); Microsoft, Troubleshooting blank screens in Windows (force-shutdown recovery loop, safe mode F5, driver rollback).