How To Diagnose Hardware Problems When Your Computer Won’t Turn On

Ads by Google

computer wont turn onLast week I showed you some of the simplest DIY repairs and upgrades that you can do yourself, but one reader asked how to diagnose which component was the problem. Today I’d like to walk you through the process of diagnosing a faulty PC that won’t turn on, then next week I’ll show you some more in-depth tools to pinpoint problem hardware in a situation where the computer will turn on, but is acting strangely.

Obviously, if the power won’t start on your PC then no amount of software tools is going to help you, so it’s time to open the case and start the hardware diagnosis process.

Strip Non-Essentials:

The first thing I do if the computer won’t turn on is to disconnect or even physically remove any non-essential system components. This includes:

  • PCI / ISA / PCI Express Cards – Anything apart from your video card (and your video card too if you have an onboard port you can use instead) should be removed, such as sound cards, networks cards, modems, additional interface cards. You may think these are unlikely to cause issues, but one of my old machines refused to boot last week because the network card had developed a fault. Removed it, and all was fine.
  • Hard disks – You need only remove the power to these.
  • CD-ROM – Again, only take out the power cable.

Having that done, try the power again. Are you seeing any activity at all? Is there a power light on your motherboard?

Ads by Google

computer wont turn on

If you get a slight burst of power but ultimately the system won’t boot, it’s possible that either your motherboard or power supply itself is faulty. It’s quite common in old PCs to find capacitors on the board itself that have literally exploded, flooding out liquid inside and causing this kind of behavior. Check around your motherboard quickly to see if you can find any traces of the dreaded “bulging capacitor” – the tops may have opened, you may see brown liquid on the  board, or it may just be bulging slightly:

why wont my computer turn on

If you can’t see any obvious capacitor problems, then move on to diagnosing the power supply.

Diagnosing a Faulty Power Supply:

A power supply is the most common component to fail along with hard drives and fans, usually down to either the moving fan inside the power supply itself or again, capacitors. However, you should under no circumstances ever try to repair a faulty power supply – the only option is to replace it. Even if it appears to be broken, there’s a very high chance that some high voltages are still stored inside. I DON’T suggest you pull out a multimeter and start trying to test various bits of it.

There are two way to diagnose a faulty power supply, one is with a spare, and the other is with a second computer. If you have a spare, trying swapping the faulty one out and the spare in. If you have a spare computer, grab the power supply out of that and try swapping it in instead. Obviously, this is going to show you straight away that the power supply is at fault. To avoid jumping to wrong conclusions though, be sure you are plugging in ALL the leads you need to. Modern motherboards need not only the large 20-pin power plug, but often additional 4 or 8 pin plugs for additional processor or video driving power. Check your motherboard manual, or look closely around the CPU fan for connectors like this. If it looks like you ought to plugging something in there, download and read through our free guide to your PC inside and out, especially the page on power connectors.

computer wont turn on

The final option is to try your suspected faulty one with another computer, but given that there is a chance it will harm the components I don’t suggest you try this with hardware you really value.

Unplugging X made it work again:

If, having unplugged everything non-essential you find your computer now boots fine, you can start the laborious process of testing each component individually. Start with the video card, then move on to additional cards and components until you find the one that’s blocking system boot.


Computers are actually remarkably good at diagnosing themselves, and will often produce their own error codes in the form of a series of beeps. Though the beep codes vary by manufacturer, you can be sure that they have something to do with either your CPU, your memory, or the video card. Check the manual or manufacturers site for codes specific to your motherboard, or you try looking at this table of generic beep codes for older BIOSes. The most common beep code I come across is a continuous series of beeps, which indicated a memory error. It could be as simple as not seating the memory in the slot correctly (and will often come out during a move).

If your computer will turn on and function correctly, but you sometimes still hear a series of beeps during use, it means your CPU is overheating, most probably due to a fan this is starting to fail. You can try to clear the gunk and dust away from the heat-sink and fan as a short term fix, but look to replacing the whole thing. I didn’t feature this in the list of easy DIY repairs for a reason and I wouldn’t recommend it for a beginner, but if you’re serious about becoming PC hardware proficient then it’s a good process to learn.

This pretty much covers diagnosing a PC that won’t turn on, so next time I’ll be showing you how to pinpoint hardware problems even if your PC is functioning somewhat, or at least getting to the boot phase.

If you have any stories of hardware woes, do let us know about it in the comments. You can also feel free to post with any hardware help you might need, but you’ll get a wider range of responses if you ask in our special Question and Answer site.

Image Credit: ShutterStock 1, ShutterStock 2

Ads by Google

11 Comments - Write a Comment



Really thanks a lot for this valuable post as i am facing 3 beep sounds from my PC and i resolved it.


Balvinder Singh

My PC has been getting a problem… Its a AMD quad core, and I have a 550W power supply… Sometimes the CPu fan creates noise. Checked it, removed all gunk and dust, still sometimes, so what is the solution to it…

And lately(2-3 days) the PC freezes(not hangs since all resources are mostly free, but freezes). The only solution left is to force restart. Then sometime I have to switch to Ubuntu, but such problem is popping up with Windows 7 only, not any other OS. How to check what part of the computer is causing the FREEZE.

James Bruce

Fans are one of the first things to fail, because of moving parts (along with PSU and h/d). I had a similar noisy fan, and ended up having to replace the CPU cooler entirely with a more efficient, silent one.

It’s not obvious if your windows problem is related, but it could be if your CPU is overheating (perhaps ubunut isnt taxing it enough).

I’m afraid random freezes can be any one of a number of things, but here are my best guesses:

1. video card – are you running on-board or separate card. if separate, update the drivers, and check the fan on the card itself, perhaps thats the one making the noise

2. run a memcheck utility to check you dont have some bad RAM.

3. if you can, swap out the hard drive and try a fresh windows 7 install. then start installing all your devices. this will help you identify if either a particular device or the drivers for a particular device are faulty



Actually, Beeping should be the first on the list. If there is no beeps coming out of your speaker, then that is the time to take out the non-essential parts.

The second most common beep code is caused by the video card.

If you’re sure that the power supply is good and you only have the motherboard and processor singled out, in my experience 90% of the time, it is the motherboard. Processor rarely quit but still do.

James Bruce

Hi Edmar, I put beep codes last because the article was prefaced around the idea of “wont power on”. As far as I’m concerned, if you’ve got a beep code then your PC is on and debugging itself, so that’s why I put it last.

I have yet to see a faulty processor though (outside of an overheated xbox360 that is).



Fab post James. I have repaired many computers over the years so wasn’t expecting much from this article. I was pleasantly surprised by your suggestions – very comprehensive and informative. Well done.

James Bruce

Thanks Carlos. You come across bulging resistors much? I was quite shocked the first one I ever saw, but then started seeing them in loads~



First things first. Check your power supply connectors. A loose power connector can prevent the computer from initially powering up or it can cause intermittent disruptions in current which will cause shutdowns.

the connectors may not have been completely secured when it was originally assembled or the last time it was reassembled. If you move your computer around much, all the jostling can loosen connectors.

Sometimes it just the simplest thing.

James Bruce

Good advice, A4084397! Y



it is nice thnkyou



Also if none of these work try moving the RAM to a new socket. I tried all these things for hours when all I had to do was move the RAM and it fixed the problem i was having.

Your comment