Computer turns on - Black screen (always)

Hey all, I just now found this forum thanks to a good friend of mine who just retired from 10 years at Microsoft. So far I LOVE the site!

Anyways, I've been repairing computers for 7 years now as my full time job.

I had a customer call me recently and I picked up her desktop and brought it back to my home office.

When you turn the computer on the hard drive boots up, the fans spin, and all the lights work. The PSU light on the back goes green, and it acts as if it's booting up.

Only problem is the monitor (plugged in and turned on) does not show anything on the screen. When I tap a button on the monitor I get "In Power Save Mode - Press key on keyboard or move mouse" - Nothing.

I put in a video card and tried that method, same issue. I reset the memory, checked all of the computer plugs, and well, I'm at a lose for words. I cannot enter the bios, enter safe mode, anything. I'm stuck with a black monitor screen.

Could this be a power supply issue or a mobo issue? If so, how can I troubleshoot further without swapping those out (time consuming)?

This machine is a HP Pavalion a1737c and runs Windows Vista.

It is using the onboard mobo video connector (until I tried a vc I put in).

Hmm... Any clues? Thanks all!

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All Answers

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Could it be...

by boxfiddler Moderator In reply to Computer turns on - Black ...

that the monitor itself is faulty? Or the monitor connection cord/connector? Or if there is a 'transformer' (probably not the right word) that sits between where the monitor plugs into the wall and where that cord plugs into the monitor is bad? Or could the connectors at the monitor itself be bad?

IOW, does the monitor work when attached to a different computer? Or, does another monitor work when attached to that computer?

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Yes yes and yes

by TECHASAURUS In reply to Could it be...

Box, yes, the monitor works. Actually I've tried 3 different monitors, and I know they ALL work. The customers monitor worked as well on their other computer (that they tested prior to calling me).

So it is not a monitor issue.

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Then it is possible that OS, post below is correct...

by boxfiddler Moderator In reply to Yes yes and yes

I have exhausted my lack of knowledge!

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You need to swap the Power Supply for starters

by OH Smeg Moderator In reply to Computer turns on - Black ...

But that doesn't mean that it needs to be fitted to the Case just that you need to unplug the existing power supply should be 2 Plugs to the M'Board and 1 plug to each drive inside the computer.

Lay the case on it's side place a Known Good Power Supply somewhere that is useful and plug in the 4 or so connectors required.

Then plug in the Known Good PS and try to turn on to see what happens.

If nothing still happens the M'Board is dead.


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by boxfiddler Moderator In reply to You need to swap the Powe ...

if the mobo is dead why does everything but the monitor power on?

To quote the OP:
"When you turn the computer on the hard drive boots up, the fans spin, and all the lights work."

edit the usual

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Not sure why PSU would work and not mobo

by TECHASAURUS In reply to Um...

Yes that's a good question. I can hear the hd and everything else boot up, this is a power supply thing, so it would be the mobo which would send a signal across the board to/from the onboard vid card and then the pci vid card.

I'll swap the PSU out tomorrow as a start.

Hmm, I don't have a mobo like this on hand, will have to go find me one.

Turns out customers computer is 25 days out of warranty from HP/Compaq, go figure, haha.

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Sounds as if HP got things right

by OH Smeg Moderator In reply to Not sure why PSU would wo ...

The ideal hardware works for the time that the Warranty is available and then fails so that the customer has a choice of paying for the repair which earns HP more money or buy a New One.

Part of the reason why I no longer sell HP products as their Warranty leaves a lot to be desired. Here with a lot of their stuff they don't repair they swap out. Good idea while UG but a terrible idea when the customer is the one paying for the Repair.

What you need to know about PS's is that they produce several different voltages and any one can fail to work. So if you can hear the HDD's spin up and see the Fans work this is telling you that the 12 Volt rail is working but tells you absolutely nothing about the 3 Volt Rail or the 5 Volt Rail both of which may not be working.

The 3 Volt Rail powers the CPU and the 5 V Rail provides power for the Drive Controllers.

Also what would happen if the PS was no longer producing 450 W but only providing 100 W to the computer? Electronic Parts can fail in such a way that they loose the ability to work as designed while still appearing to function.


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volt meter?

by TECHASAURUS In reply to Sounds as if HP got thing ...

Hmm, I can try my volt meter? no?

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Yes not a problem

by OH Smeg Moderator In reply to volt meter?

If you don't have the Pin Out of the ATX Connector I'll post back with one. But Antec should have this in their Web Site.

But you still need to confirm that the Ampage is correct. This is something that Power Supply Testers don't actually cover. It keeps you on your toes.

I used to work on HP units that they couldn't repair years ago and I routinely found Faulty PS's that where incapable of powering the unit. This was more common if parts had been added though. I remember one Evo that worked for 6 months with a Optical Drive & Video Card added and no matter what HP changed it didn't start working again. When it was sent to me I plugged in a 450 W Antec PS and the thing sprang to life. Not sure what HP here did to fix it though as they had already changed 5 PS's and the M'Board a couple of time. I presume that they either continued to change PS till they found one that worked or they removed the extras and told their customer they these where no actually supported though without a Optical Drive I'm not sure how the Customer was supposed to reload the thing when that became necessary.


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Go figure - Thanks HP

by TECHASAURUS In reply to Yes not a problem

Go figure, thanks HP.

No wonder I own an Alienware as my personal prior to Dell buying them.

5 years old and not one problem ever!

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