# computer won't boot up - switch or power supply?



## JimG

I have a HP Desktop that fails to boot up.  I have a power led on the back that glows when first plugged in, but goes out when I push the on/off switch.  If I unplug it for a few seconds, the led flashes once.  Then when I plug it back in the led will stay lit until I push the on/off switch again whereupon the light immediately goes out and the computer fails to boot up.
I'm sure it must be a bad power supply (short?) or the switch.  Is there a way to test which it is myself or do I need to take it to a shop?
Any help would be appreciated.


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## deanj20

> I have a power led on the back that glows when first plugged in, but  goes out when I push the on/off switch.  If I unplug it for a few  seconds, the led flashes once.  Then when I plug it back in the led will  stay lit until I push the on/off switch again whereupon the light  immediately goes out and the computer fails to boot up



Waaa? 

I imagine it's the PSU. I don't know what the LED indicates or how it works, but if the switch is in the "on" position, and the computer isn't getting power, it's likely the PSU. 

They do sell power supply testers. Or you could take the PSU apart and bypass the switch (I'm assuming you're talking about the switch on the PSU, not the power button for the computer). If you don't feel comfortable doing that, then take it to a shop.  I would just swap it out w/ a known-to-work PSU, but I'm guessing you don't have one laying around.


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## blazin8556

change the psu and see if it works.


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## El Gappo

So your computer refuses to show anything on your monitor, turns on but doesn't boot, and is making a weird noise at you?
Either your monitor isn't on, or this is a P.O.S.T Failure. (Power On Self Test).

Some more recent motherboards don't use a speaker, but a small LCD readout, consult your motherboard's manual.

A POST failure can be caused by several things, such as: incompatibilities, and/or electrically shorting out your components. I'm presuming that you haven't tried installing an i7 into a K8 motherboard, so I'm not going to go through that. 

Important: If you turn on your computer and nothing happens at all, then that is not a no POST issue, it's a power issue. If this is the case, then you've got the wrong thread.

If you have recently added new components prior to the no POST then remove them now. If this solves your issue, then the new hardware is likely incompatible, or you need to change some system settings to get it to work. 

If you're adding a new CPU, sometimes you need to do a BIOS update.

Remove anything from the I/O panel that isn't necessary. Basically, unplug everything except your trusty keyboard. (And monitor, duh).

*This is where things can get tricky.*

*1.)* Check your power connectors haven't worked their way loose, make sure they are fitted securely to the pins on the motherbard and that none of the spare pins (standoffs)are shorting out on your case. If this is the issue, tape up the spare pins. While you're here, you can reset the CMOS jumper/push the button. If it still doesn't work, remove the motherboard battery for 10 minutes to be safe, then plug it back in.]

*2.)* If you get more than one beep when turning on the PC then consult your motherboard manual, or phone your motherboard manufacturer's tech-support. Most motherboards' beep codes are different, but usually this is correct.

*3.)* Is your heatsink's fan spinning? If it has failed, the motherboard's safety features likely shut down the computer to save it from overheating. Also, it's worthwhile checking that it's seated correctly, without wobbling. 

*4.)* Time to unplug everything you don't need from the motherboard, Optical Drives, Hard Drives, Video Cards, etc., if this solves the problem, plug them back in one-by-one until you can eliminate the culprit. (If you have no onboard video, the speaker comes in handy here, or you're going to need a spare). 

*5.)* So you're still here? Remove all but one stick of RAM, still fails? Try all your sticks of RAM individually, if you've still got no POST, check for short caused by something interfering with the back of the motherboard, loose standoffs, etc. It's best to remove the motherboard from the case entirely and place on a cardboard box to be safe, also makes these checks quicker and easier to do.

*6.)* Check your PSU is powerful enough for your system. Don't try and run a HD4890 and an i7 on a 250W PSU; that's never going to happen. Check out the specifications on the manufacturer's website and check how many watts you have available on the 12V rail, (If you're stuck, remember P=IV, Power (Watts) = Current (A) * Voltage (V)). Check for power consumption of your components, mainly your video card(s) and CPU.

*7.) *If you're still reading this, you've got a dead component. A testbed/working motherboard + PSU will come in handy when finding exactly what is wrong. Don't get too angry and start throwing things out of windows, make sure you know what's broken by process of elimination (If it works in another rig, it's not the culprit.), only then can you start baking components.  

*8.)* Oh, make sure your display isn't set to onboard in the BIOS when you have a dedicated GPU in... that would be silly now, wouldn't it? ​
useful links : the bios beep code table http://www.pchell.com/hardware/beepcodes.shtml
and the psu calculator http://extreme.outervision.com/psucalculator.jsp

Let me know if I forgot anything, 
Is this how you are meant to reply to help threads?


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## 2048Megabytes

The problem likely is a bad power supply but it also could be something else.  A faulty motherboard could also cause the problem.


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## Atrosity

It's your PSU


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## September

I just installed a new power supply of higher wattage in my old PC.  The old power supply still works and stills runs the unit.  The new power supply will not start the unit.  I push the on button and the blue light flickers and the unit shuts down.  It is like a short out.  I had the new power supply tested and it does work.  It just won't run my PC.  I put the old power unit back and everything runs perfectly again.  What could be wrong with the way I am installing the new power supply or is it incompatable with my old PC?


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## 2048Megabytes

A faulty motherboard could also be the cause of this problem.  How old is the motherboard?  Is it still under warranty?


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## OverClocker

that what really happened to me in my work ..boot up off/on power supply . it will never load to windows. All i have to do is that I reformat all up. The window was corrupted that why it will never load to the window.


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## nonsense_silly

*Did You Figure This Out?*



JimG said:


> I have a HP Desktop that fails to boot up.  I have a power led on the back that glows when first plugged in, but goes out when I push the on/off switch.  If I unplug it for a few seconds, the led flashes once.  Then when I plug it back in the led will stay lit until I push the on/off switch again whereupon the light immediately goes out and the computer fails to boot up.
> I'm sure it must be a bad power supply (short?) or the switch.  Is there a way to test which it is myself or do I need to take it to a shop?
> Any help would be appreciated.



Did you ever figure out if this was simply a bad power supply?

Thanks,
Greg


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## Okedokey

If you have a faulty motherboard and it doesn't send a 'good' signal to the PSU it wont turn on.


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