Most of us leave our computers running pretty much all the time. Unless there is some major update or you’re going to be away for a few days there’s not much reason to shut them off. That said, when you sit down to your PC and find that it *is* off, generally the first instinct is to press the power button and hope for the best.
What about when it doesn’t turn back on?
Warning
As always, a word of precaution. What I’m going to tell you may disagree with your manufacturer warranty, and will require tools. If you don’t feel comfortable opening your desktop PC, please consult a trusted professional. Finding a “warranty void if removed” sticker means you should make absolute sure the system is no longer covered by warranty before removing it. If that was all blah blah blah to you, read on.
Power switch
No power? Well, let’s make sure it is *getting* power first. Check the back of the machine, locate the power cord. Make sure that is plugged in firmly on both ends, and (assuming you’re connected to either a power strip, surge strip, or some manner of battery backup/UPS) that the power source is getting power. If all of that checks out, look at the power supply itself. Check the switch, make sure it is in the ON position. The side with the line should be down, the circle should be up. Flip it to the correct position and press power. If it lights up, you should be good to go (a basic diagnostic makes a good follow up, just in case anything was affected by a random switch-off)
How to access and test the power supply
If the cords and switch are plugged and set correctly but you still don’t get power, time to see if the power supply has failed. For this, you will need a screwdriver to remove the side panel. There are a couple of ways to test the power supply. You can perform either a basic check using a multimeter on the continuity or resistance setting, a more accurate check using a power supply tester, or if you have access to spare parts you can connect a compatible power supply and see if that resolves things.
The multimeter testing method
For the multimeter, probes go into the green and any black wire. This is a basic check but does not verify all voltage rails or ability to handle a load. Unplug all connections from the power supply to the motherboard (usually 2 plugs) and the drives. Using the main power connector (20 or 24 pins) from the power supply, insert probes, plug in the power cord and flip the switch. If you get nothing, you have a bad power supply.
The power supply tester method
For a power supply tester ,results will vary by model. We recommend using one with has many functions as possible for a more accurate reading. Our repair bench uses the Thermaltake Dr. Power II and it does an excellent job of verifying the correct and stable voltages on all connection types from the power supply. It is designed for quick verification and should not be left connected for extended periods of time.
The swap the power supply method
IF you want to replace the supply and check that way, make sure you only connect what is necessary to get the system to give display at first. If you have more problems and you connect everything you are just wasting time. Note that this is the most effective way of diagnosing a bad power supply since neither of the previous methods apply a full load to the power supply.
Testing the motherboard
So what if the power supply is good – or you replace it and it still won’t power on? Then the problem is most likely the motherboard. There’s a little known trick for testing that too. Reconnect good power to the motherboard and make sure that you have a speaker on the motherboard or connect one according to the manual. Now remove all the memory sticks and power the system on. If the system beeps multiple times complaining of no memory, the motherboard is very likely good.
Running out of options
So what if both the power supply and the motherboard test good but the problem remains? Swap the power supply to ensure it can handle the system load. If it still doesn’t power on, you will hopefully be getting some beep codes that with research can indicate the failure. If not, it’s definitely time to get help.