Dell has an article titled Resolve No Power, No POST, No Boot or No Video Issues, and its desktop steps are specific. Computers have an LED that glows when receiving power, and on a desktop it sits on the front panel near the power button. If there is no power: reseat the power cable at the back and the outlet, bypass power strips, extension cables and protection devices, check the outlet with another device, use a verified working power cable and make sure the main and front-panel cables are seated on the board.
Dell's desktop power supplies carry a built-in self-test: connect the power cable and press the test button beside the AC plug, and if the supply LED does not light, remove the supply cables from the board and test again; if it still does not light, the supply is probably faulty, and if it lights, one attached component is at fault, found by reattaching them one at a time. If the desktop shows the Dell logo but never moves on, or an amber power light, it has probably failed its power-on self-test; note the LED or beep pattern. Tap F12 at the logo for Dell's diagnostics.
Differential
Likely causes of “Dell OptiPlex 7020 will not turn on or start”, and how to tell them apart
- 1
No power at the tower
What separates it There are no lights and no fans because there is no power at the tower
How to confirm Reseat the power cable, bypass power strips and try a verified working cable and outlet, as Dell's guide says
- 2
A power supply fault
What separates it The cable and outlet are fine and nothing lights
How to confirm Use the power supply's built-in self-test button; if the LED stays dark, the supply is probably faulty
- 3
A component or accessory fault
What separates it The supply test passes with the cables off the board but fails with them on
How to confirm Reattach components one at a time, as Dell's guide describes
- 4
A failed power-on self-test
What separates it The Dell logo stays, the power light is amber or a beep pattern sounds
How to confirm Note the pattern and follow Dell's diagnostic indicators; run diagnostics from F12
- 5
A startup or update problem
What separates it The tower starts and shows an error or a repair screen
How to confirm Use Startup Repair from the Windows recovery environment and let it complete
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether the front power light comes on, its color and any beep or LED pattern
- Whether the outlet, cable and power supply self-test work
- Whether the tower was moved, opened, upgraded or hit by a power cut
Try in this order
0 of 7 completedCheck the cable and outlet
ReversibleReseat the power cable at both ends, bypass power strips and test the outlet with another device.
Check the front power light
ReversibleCheck the front power light, since a lit LED on the front panel means that power is reaching the machine.
Try the power supply self-test
ReversiblePress the test button beside the AC plug and see whether the supply LED lights.
Remove everything
ReversibleUnplug drives, USB devices and the monitor cable, then reattach parts one at a time.
Read the lights and beeps
ReversibleRead the lights and beeps, and note the pattern and look it up in the OptiPlex diagnostic indicators.
Run the diagnostics
ReversibleRun the diagnostics, and if the tower powers on, tap F12 at the Dell logo and choose Diagnostics.
Try recovery
ReversibleIf it starts to a repair screen, use Startup Repair and let it run to the end before you try anything stronger.
Model-specific
What is true of this model and not of its siblings
- Diagnostic indicators
- Dell publishes a separate article of diagnostic indicators for OptiPlex desktops, and beep codes for desktops, which decode LED and beep patterns.
Stop boundary
When this stops being a self-service repair
- !If the power supply self-test fails, contact Dell Support with the Service Tag for a replacement
- !If it smells of burning or trips a breaker, stop and take it to service
- !If it starts to a repair screen, see the startup recovery page
Evidence ledger
Sources behind this answer
Dell's guide with the desktop power steps, the power supply self-test and POST indicators.
Power and accessories for a blank screen.
Startup problems.
The Dell OptiPlex business desktop line.
Exact questions
Common questions
How do I test the power supply?+
Dell's guide says each desktop supply has a self-test: with the power cable connected, press the test button next to the AC plug and see whether the LED lights. If it does not, remove the cables from the board and test again.
Should I bypass the power strip?+
Yes. Dell's guide says to bypass power strips, extension cables and protection devices to check the tower powers on properly.
What does a Dell logo that never moves on mean?+
Dell's guide says the computer has probably failed its power-on self-test. An amber or orange power light points the same way; note any pattern.