# HP pavilion t490 power light flashing - won't start



## flyboy50

Hi,
I have a problem with my HP t490.fr : Before leaving on vacation, I turned the electricity off in my apartment. When I came back, I wasn't able to turn the computer back on. There is a little green light in back of the PC that should be on steady, instead it is flashing and there's a faint clicking noise like from a relay. 
From what I understand, this could either indicate a PSU problem or a problem with the CPU, motherboard or some other component linked to the motherboard. When I disconnect the power supply to the mainboard, the light comes on steady, so I don't think it's a PSU problem.

I had the exact same problem about 2 months ago, after a power outage. A repair guy picked up the PC and "measured it through" and miraculously got it to work again, without changing any parts. He suspected a problem with the motherboard and recommended to replace it. I wanted to see if the problem would reappear before doing so - I think I'll definitely have to replace the motherboard now - but I was wondering how he fixed the problem and if I could get the machine to work again, until the new motherboard arrives and is put in, in order to minimize the downtime.

Btw, I tried unplugging the power supply to the drives, motherboard and graphics card, and removing and putting back the graphics card and RAM - but that didn't fix the problem.

Any ideas ? Thanks in advance.


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## TheMatt

Hi, and welcome to TSF! :wave:


I would actually suspect the power supply is the issue since HP usually doesn't give power supplies with enough power. See if you can borrow a PSU to test.

When you plugged in all the connectors, did you remember to plug in the 4-pin (2x2) ATX12v CPU power connector?

Also, what graphics card do you have in the AGP slot?

Also, have you tried clearing the CMOS?
http://h10025.www1.hp.com/ewfrf/wc/...c=en&cc=us&dlc=en&product=391933&lang=en#N895


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## flyboy50

Thanks for your reply, Matt..
The CPU power connector is in place, that's not it. The graphics card is an ATI 9000 series, I think, but I don't know which model. I tried clearing the CMOS as well - still the same.
All I know is, the first time this happened, the guy from the repair service could fix it (temporarily) by just isolating the components and checking them. I don't know much about computer hardware, I wouldn't know how to isolate the CPU, for example. The repair guy will stop by tomorrow morning, maybe he can do his magic trick again - either way, I'll post when I know more, looks like more people have had problems of that kind, maybe it helps. 
Thanks again !


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## TheMatt

If he stops by, ask him what he did last time. Good luck.


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## Doby

I agree with Matt thats a power supply issue

http://h10025.www1.hp.com/ewfrf/wc/document?docname=bph06788&cc=us&lc=en&dlc=en&product=391933&dlc=en&lang=en#bph06788_section_2

Scroll down to "Power supply light on or flashes"


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## babonim

Yay for me! Hopefully this will help someone else out. As I read from other people, they thought it was the power supply. I did too at first. A few others said that they had their computers not work after a storm or an electrical surge, even with a surge protector. I do believe it is an issue with the motherboard.

I was looking at a friends computer that was put out by a storm. When unplugging the all power connectors to the motherboard (and all drives), and then plugging in the power supply to the wall the green light would then stay on. This of course made the next course of action to plug in the main power connector (the one longest rectangle one) to the mother board while the power supply is plugged into the wall. 

Viola! 

Just as the power surge from a storm knocked it out, a little surge to the motherboard breathed back life to the computer. While this is a bit of an unorthodox method to get a computer to work again, it sure beats buying a new mother board, or buying another power supply to have the same result.

Hope this helped

It sure would positively reinforce me, if some people gave feedback if this works for them.


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## tech0001

I have encountered the same problem. Resetting the mobo power cable fixes it but if you unplug the PC power from the wall, wait til the Green light goes out on the PS and then plug it in again it same problem, flashing Green light - until you go inside the case and reset mobo power cable again. Then the light is stready and the unit powers up again. I'm guessing this is a mobo problem but unsure. Any thoughts would be appreciated. Thanks 




babonim said:


> Yay for me! Hopefully this will help someone else out. As I read from other people, they thought it was the power supply. I did too at first. A few others said that they had their computers not work after a storm or an electrical surge, even with a surge protector. I do believe it is an issue with the motherboard.
> 
> I was looking at a friends computer that was put out by a storm. When unplugging the all power connectors to the motherboard (and all drives), and then plugging in the power supply to the wall the green light would then stay on. This of course made the next course of action to plug in the main power connector (the one longest rectangle one) to the mother board while the power supply is plugged into the wall.
> 
> Viola!
> 
> Just as the power surge from a storm knocked it out, a little surge to the motherboard breathed back life to the computer. While this is a bit of an unorthodox method to get a computer to work again, it sure beats buying a new mother board, or buying another power supply to have the same result.
> 
> Hope this helped
> 
> It sure would positively reinforce me, if some people gave feedback if this works for them.


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## tech0001

Update:

Tested different PS and unit worked fine. Replaced supply and all is well.


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## mle3131

My computer also will not come back on after an unexpected power outage. The green power light flashes quickly. My son had a computer that he does not use so I thought I would switch out the power supply until I realized they weren't the same size. So, if I have read the above post correctly, I can try unplugging the power supply from the wall. Disconnecting all of the wires that the power supply connects to inside the computer, reconnect all but the main power supply to the motherboard, plug the power supply back in to the wall, then plug the main power supply to the motherboard and that may boost the power back on to the computer?


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## Wrench97

mle3131 said:


> My computer also will not come back on after an unexpected power outage. The green power light flashes quickly. My son had a computer that he does not use so I thought I would switch out the power supply until I realized they weren't the same size. So, if I have read the above post correctly, I can try unplugging the power supply from the wall. Disconnecting all of the wires that the power supply connects to inside the computer, reconnect all but the main power supply to the motherboard, plug the power supply back in to the wall, then plug the main power supply to the motherboard and that may boost the power back on to the computer?


NO do not unplug and replug the motherboard with the psu plugged in that may cost you a motherboard.


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## estephanz

Thanks babonim your post saved my computer as well, I just did what you suggested and it worked great for me, now my computer is back to life and working again since yesterday, I strongly recommend that people having exactly such an issue (flashing green LED on the power supply after unplugging the computer from the wall socket for a while) to try this out before buying a new power supply or motherboard, it worked like magic for me eventhough I tried all other rescue tips (from this forum other ones and even HP) like removing all plugged in cables from the mother board, resetting CMOS ... nothing worked and it was the same **** same story until I used the method that babonim described !!! Thanks again babonim !!!
My computer model is an old HP Pavillion a340 ... It's a five years old computer but I changed the motherboard on it like 2 years and a half from now, so it's definitely an issue with the PSU more than the MOBO.



babonim said:


> Yay for me! Hopefully this will help someone else out. As I read from other people, they thought it was the power supply. I did too at first. A few others said that they had their computers not work after a storm or an electrical surge, even with a surge protector. I do believe it is an issue with the motherboard.
> 
> I was looking at a friends computer that was put out by a storm. When unplugging the all power connectors to the motherboard (and all drives), and then plugging in the power supply to the wall the green light would then stay on. This of course made the next course of action to plug in the main power connector (the one longest rectangle one) to the mother board while the power supply is plugged into the wall.
> 
> Viola!
> 
> Just as the power surge from a storm knocked it out, a little surge to the motherboard breathed back life to the computer. While this is a bit of an unorthodox method to get a computer to work again, it sure beats buying a new mother board, or buying another power supply to have the same result.
> 
> Hope this helped
> 
> It sure would positively reinforce me, if some people gave feedback if this works for them.


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