The light's on, but nobody's home

[EricKei]

I have an odd issue...

Relatively new comp (self-built, back in April or so). Working fine yesterday morning. Last night, I come in, nothing. Nada. No response to power button.

As I'm owned by a couple of cats, the first thing I did was the sniff test, to make sure that one of them hadn't shorted the board out like my last system. Fortunately, nothing there.

Checked Power supply, all connections, etc. The little green light on the mobo comes on, which suggests that it's getting power just fine.

I suspected the power switch, so I swapped the Power and Reset button wires with one another and tried that. Nuthin'.

I don't even get error beeps from the mobo; I even double-checked to make sure that the little internal speaker was installed properly.

I have not added any new hardware since early May, no new software. The only odd thing was a memory error -- two months ago. I ran memtest, it showed that I MAY have a bad stick of RAM --- this is as good a time as any to RMA it, I suppose ~_~ --- but would a bad stick prevent the BIOS from loading and throwing out a beep code?

Brief specs:
ASUS P7H55-M PRO mobo
i3-530 cpu
2x2gb of ddr3 g-skill ram, they're dual-channel (which means I may or may not be able to run a "one stick of ram only" test)
GeForce GT240 video card
750w PSU

thanks for any advice youse guys can offer

[crashhelmet]

Does the PSU fan kick on at all when you press the button? Any fans inside the system for that matter?

If not, i'd start with doing a voltage check on the PSU to make sure it's putting out the required +5, +12, & +3.3 if my memory serves me right.

If they all pass, only thing i can think of at this point would be the board.

If fans are spinning, I'm looking at the board, CPU, or RAM as being a possible fault. Gets into PITA troubleshooting, IMO, but it's where you gotta start.

CH

[EricKei]

No fans even attempt to kick in at all

PSU has been working just fine for 4 months with no issues; I don't have a tester, but here's what I've done so far:

Removed cmos battery, EVERYTHING unplugged (not even drives are plugged in), replaced it with a fresh battery an hour later. no luck. Removed RAM, nada, reseated ram and tried the other pair of slots, nada, tried just one stick, nuthin.

Will try without vid card (mobo has onboard vid); no sound card to remove, it has built in. No other cards to remove

I'm this close to taking it down to the local comp shop and just having them test everything. will do that if I can't get it up tonight

[lordlundar]

PSU is dead, get it replaced.

Same thing happened to my aunt's machine last month. Exact same symptoms.

[barcode]

I'd guess the PSU as well. Quick explanation:

Most PSUs have different supply buses (rails) for each of the voltages. Typically, you'll have the +12, +5, +3.3, -12, -5, and +5VSB. It's the +5VSB that's the odd rail here...

Modern PSUs, to get the Energy Star rating and provide for better control, allow themselves to be placed in various modes. The main rails are usually switch-mode versions, which provide for high power with minimal waste. In order to control the main rails, they also have to power the circuit(s) that control them (otherwise, there would be no power to the controller to tell the rails to power up). This is where the +5V Stand-By rail comes in. It's typically the older linear-mode type, which provides about an Amp or two to the mobo circuitry so you can wake it up from a power-down mode, sleep, or hibernate. This is why you see the glowing LED on your mobo - it's letting you know that the +5VSB is working, and that there IS power applied to the mobo, which MAY be used by your memory or CPU if you're in one of the sleep modes.

When activated, the PSU will then power-up the other rails. Because of this split-rail design, you can easily lose an entire rail (or entire switching section) and still have that mobo LED lit.

(Note that some PSUs are pure junk, and will use the +5V rail to supply the +3.3V rail - if the label says "Combined current of +3.3V AND +5V is NOT to exceed...", then you have one of these crappy models.
For a rating of very good and bad PSUs, visit http://www.HardOCP.com )

If you're lucky, then you have one of the better models, which MAY have just blown a fuse for the switching section due to age or overload. Some PSUs will have something called a "resettable fuse". All you need to do is unplug the PSU for about a minute, and it'll reset itself. If you've already done that, then you probably have a standard fuse. Another thing to check before dropping $ on a new one is to check your mobo manual and see if you have any USB ports jumpered for "Always ON/Standby" operation. This may draw too much current from the +5VSB supply, and make it so it's not picking up the command to power-up. By jumping these to OFF, you'll be disabling any keyboard or mouse power-on options, but the button should still work.

Hmmm. Looks like I lied about this being "quick"...

Anyway, if you do plan on opening the PSU, remember that the one thing ALL manufacturers get right is the big yellow label that warns you of high voltages and possible death if you touch the wrong things. However, it's the only way to check a standard fuse (looks like a small white ceramic cylinder about 5mm x 20mm) and tell if the capacitors inside have failed - visit http://www.badcaps.net for info.

Oh, and if you have bad memory, there's enough cache on the CPU to allow it to boot, and give an error beep (or ten) to let you know about what went wrong during the POST. If the CPU is bad, then there's nothing to make anything beep, but at least the fans and drives will power up. Hence, we're guessing PSU.

barcode

[lordlundar]

Hmmm. Looks like I lied about this being "quick"...

I've found any technical explanation outside of "The computer went kablooey" never is quick.

Anyway, if you do plan on opening the PSU, remember that the one thing ALL manufacturers get right is the big yellow label that warns you of high voltages and possible death if you touch the wrong things. However, it's the only way to check a standard fuse (looks like a small white ceramic cylinder about 5mm x 20mm) and tell if the capacitors inside have failed - visit http://www.badcaps.net for info.

That said, PSUs are cheap enough to replace so it's usually not worth the risk or effort. I say try a new one on a safe power line and if it boots up, toss the old one.

[EricKei]

Thanks for the impressively detailed explanation o_O But.....^_^;>

I took it down to the chop shop, and it turned out that the power button itself had shorted out (on a 4 month old case...). They rerouted the wires (I had just swapped where they plug into the mobo before, didn't help, so they must have done something more in-depth)...and, long story short: My - heretofore unused - Reset button now turns the computer on

[Chromatix]

If the power button was shorted out, and you had it plugged into the reset connector, then it would have been holding the computer in reset mode.

This doesn't explain why the fans wouldn't turn on though. Or did they?

[EricKei]

They did not.

Actually, it does explain the fans not working -- The system never had a complete circuit to allow the electricity to REACH the fans, due to the short. Or do computers these days work that way? >_> Either way, the mobo never got the "OK to turn on message".

[lordlundar]

If the power button was shorted out, and you had it plugged into the reset connector, then it would have been holding the computer in reset mode.

This doesn't explain why the fans wouldn't turn on though. Or did they?

You misread. The Power button is shorted out and the techs plugged the reset button into the power on jumpers. The issue was that the power button was not able to complete the circuit to start the boot up cycle.

[Eric the Grey]

Couldn't they just replace the power button? I know I've seen them in shops. . .


Eric the Grey

[lordlundar]

Couldn't they just replace the power button? I know I've seen them in shops. . .


Eric the Grey

Depends on how it's mounted. A number of ones I've seen would require extensive damage to the front panel just to get it out. In that case, if you're that determined to get a new one, you might as well order a new front panel. (besides, these days the only difference between the power switch and the reset switch is the audible 'click')

[barcode]

I took it down to the chop shop, and it turned out that the power button itself had shorted out

Right now, my dad's voice is echoing in my head...

"It's always something stupid..."

On the other hand, at least you'll have a... "plethora" of information the next time this happens to you, huh?

barcode

(Off to re-cap and re-fan a throw-away PSU...)

[roothorick]

Anyway, if you do plan on opening the PSU, remember that the one thing ALL manufacturers get right is the big yellow label that warns you of high voltages and possible death if you touch the wrong things. However, it's the only way to check a standard fuse (looks like a small white ceramic cylinder about 5mm x 20mm) and tell if the capacitors inside have failed - visit http://www.badcaps.net for info.

Before you open the PSU, call the manufacturer, give them your PSU's serial number, and ask about warranty. Opening that case will void the warranty, even if it's just to replace a fuse -- and if it's something more sinister, and it IS in warranty, you just got a new PSU for free.

[EricKei]

Just as a follow-up: Some light searching has revealed that this particular box (lian li/lancoool Dragonlord PC-K58) is known for this specific defect -- shitty power connectors -- but it is otherwise really solid.