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

Last 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?

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:

 

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.

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.

Beeping:

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.