If your computer won’t power up when you press the power button, the fault is probably one of three things:-

1) The power button itself is faulty.

2) The motherboard is faulty.

Or, more than likely;

3) The power supply unit ( PSU ) has failed.

Did you notice a burning smell last time you powered up your computer? Did you see smoke and/or flames at the back of it?

If so it’s likely that your PSU has burned out.

Is the power supply’s fan still working?

If not then it’s most likely that your PSU has burned out.

If this is the situation with your computer, then I’ll be 100% honest with you from square 1: Your computer may or may not be seriously damaged.

The PSU supplies power to each component part of your computer. Most of those component parts are very sensitive. There is a chance that a high-voltage spike from the PSU as it died has fried something critical inside your computer: The CPU, for example, or the RAM. Maybe the graphics processor on the graphics card.

- So it’s always a good idea, if you have definite suspicions that your power supply unit is playing up, to replace it, in order to prevent this situation from happening. Normally if you catch and replace a PSU before it fails there is a lot less chance of it damaging other components.

*I have to say it just to cover all the bases: -

If your computer appears dead; check the following before you do anything else: -

*Is the power cable plugged into both the wall socket and the power supply?

*Is the fuse in the UK 13 amp plug (BS1363) (If you’re in the UK.) working? 

*If you’re using a power strip or surge protector, is it turned on and working?

*Is the on/off switch on the rear of the power supply switched on?

*Is the 110/220 Volt switch set to the correct setting? In Europe it should always be set to 220 volts. If it’s set to 110 volts in Europe it’ll destroy your PSU and probably fry most of the other circuitry too in the process. In the USA, it should be set at the 110 volt setting. This is due to the Americans using 110 volt AC mains voltage; whereas most of the rest of the world uses approximately 220 volts AC.

What to look out for

Is the CPU fan extremely dusty/dirty/manked out with dust and/or making unusual noises? If so then, whilst it’s possible to remove the PSU, open it up, and clean it out + lubricate/replace the fan; I don’t recommend this for anyone not familiar with the innards of a PSU. Why? Because there are high voltages inside the PSU, even when it’s switched off and disconnected after operating. These charges are stored in the capacitors inside the unit, and can, in some instances, take days to discharge. Also it’s very fiddly precision work that could take up a lot of time. It’s always a better idea to replace the PSU completely.

If the fan fails to turn properly the PSU can and will eventually overheat and burn out. This could be anything between the same day and possibly next year; but you can rest assured that it’ll happen, and probably at the most inconvenient time.

Does your computer shut down unexpectedly at times? If so then there may be any of a number of issues affecting it. First check that the issue isn’t software-oriented: A file-system error may be the cause, or possibly data corruption, even a malware issue perhaps? (See this article for details of how to fix file system and data corruption issues.) If it’s not a software issue then quite probably the cheapest one of the hardware issues to rectify will be the PSU. Even if replacing it doesn’t solve the problem, at least you know that you now have a brand new PSU installed. If it does solve the problem then it probably cost you less than replacing the RAM and/or the motherboard would have done; which would have been the next steps.

How do I replace a PSU?

Fortunately doing so is not as difficult as you may imagine: Just be sure that the unit you replace it with is as good or better quality than the unit you replaced. Some cheap and nasty power supplies are not what they seem. See this article. I suggest that before you replace a PSU that appears to have already burned out, you check its output first, before replacing it, as the reason that your machine appears dead my not always mean that the PSU is the faulty component part.

You can see where the PSU sits inside the case before you open it: Look on the back of the case and you’ll see the electricity mains power input and the opening for the power supply fan in close proximity. Now open up the case and identify the PSU: – A metal box with coloured wires that connect to the motherboard and other components. Make a note of where each one is connected: It’ll make it easier to reconnect then efficiently later, when you’ve replaced the PSU unit.

Ensuring that the computer is disconnected from the mains electricity, remove all the plugs on the ends of the bunches of wires that issue from the PSU from their sockets on the computer’s components. Be gentle and don’t force anything: if it wont budge then there’s probably a clip holding it in, or it might need a bit of gentle coaxing. (It would be a good idea to connect your body to electrical earth with an antistatic earthed wrist strap before starting this entire operation; just to be on the safe side.)

The power supply is normally mounted in the case and secured with four screws on the back of the case. Remove the screws and gently urge the PSU out of the case, ensuring that any of the trailing coloured wires don’t catch on anything and damage it. You might in some cases find that the PSU’s removal is obstructed by (an)other component(s). if this is the case it may be necessary to remove those components also. Don’t freak here: if you don’t feel able to continue you’ll have to ask a geek for help. Don’t lose the screws; put them somewhere safe. (I have screws lurking in every corner of the room where I neglect to keep them safe at times.) Having got the old unit out, discard it. Recycle it if at all possible. (ROHS)

Most PSUs these days are ATX type. If you have an old AT type PSU fitted to your computer then I suggest that you simply bin the computer and get a new one due to its age, or you give or sell it to a museum if you can. (Remember to delete the data on the hard-drive first.)

You’ll need to buy a replacement PSU with identical or higher ratings than the old one. Higher ratings would be a good idea in case of future expansion. (Adding more components.) I suggest ordering online, as shops and department stores may add extra cost simply to help keep their plush showrooms running.

Installing the New PSU

Insert the new unit into the space from which the old unit came and screw it into place using the four screws you took from the old unit’s mountings. You’ll normally need a Phillips screwdriver to do this; just as you would have required to remove them in the first place.

Next; find the ATX (P1) power connector and firmly plug it into the motherboard’s ATX receptacle.

Plug the SATA or Molex power connectors into the hard drive, cdrom drive, and all other components, as appropriate, (See your notes that I advised you to take previously.) that were previously connected to the power supply’s outputs.

*If a component has both a SATA and a Molex power connector, only connect one or the other. Connecting both will destroy the component and probably your new PSU also when you power up.*

Make sure that there are no unused power connectors hanging around in the case where they could touching a fan or anything metal. Use twist-wires or cable-ties to secure any such connectors securely to the case without allowing them to electrically connect with the case. See this article.

Replace the case panel and reconnect the monitor, keyboard, mouse, speakers, etc.

Check the On/Off and 110/220 switches (if present) on the back of the power supply to make sure they are in the correct position – Remember: 220 volts in Europe; 110 if in the USA or anywhere else where the mains input voltage is 110 volts. *If in doubt; start with the switch set at 220 volts and if it doesn’t work, try 110 volts. – unless you’re in Europe, in which case something somewhere’s not connected if it doesn’t work. *I repeat: DO NOT attempt to set the switch to 110 volts in Europe. – Otherwise you will hear a bang and your computer will be toast.

Insert the power cable’s “kettle plug” into the socket on the back of the power supply, plug the other end into your wall socket or power strip, and power up as normal. Everything should work properly and your PSU is no longer dodgy.

Your comments are appreciated.