[Mongoose]

My family has a Dell Inspiron 518 desktop system that's two or three years old, with a Core 2 Duo processor, 4 gigs of RAM, and a dedicated video card that I can't remember at the moment, and running Vista Home Ultimate.  It gets the typical sort of family usage: Internet, e-mail, word processing, pictures, the usual.  Pretty much the most intensive workout it gets is my brother playing random Flash games, but that's about it.  Anyway, my mom mentioned this morning that the computer wasn't turning on at all when she pushed the power button...even I can figure out that this is a Bad Thing.  So I try it myself, and sure enough, she's right...when I hit the power button, there's no fan spin-up, no error beeps, no lights on the front of the case, nothing.  I start by unplugging it for a while and then trying again, but no dice.  I then remove the cover and give the interior a decent vacuum/air can treatment, but again, nothing.  The green LED on the back of the 300W power supply is on, so that's receiving power at least, and the amber LED on the motherboard itself is glowing solid too, so something's getting through there, but it's obviously not enough to actually get anything moving. 

Then I remember that, randomly, I actually have a spare 500W Antec PSU that Stealth awesomely sent me when he gifted me a video card...the thing wound up not physically fitting in my asinine old Dell case, but I've held onto it in case I feel like buying a new case to transfer my own system over.  So after some fiddling around and jamming my fingers into too-small gaps between components, I manage to unplug the main power connector and what I assume is the ground cable from the motherboard, and attach the ones from the Antec PSU in their place.  I hit the power button...and success, I make it through the BIOS screen!  After reconnecting the keyboard (there's something almost profound about the "Keyboard error.  Press F1 to continue." message), I'm able to get the system to the "Boot media not found" screen, which is expected.  (The Dell PSU has these flat elongated power connectors for the HDD and DVD drive, which I guess are standard SATA, while Stealth's PSU has this connector with four larger holes in it, so I couldn't hook those up.  How's that for using technical terms?)  I didn't take the Dell PSU out completely, since there's this one wire for the USB connectors on top of the case that is a real ***** to deal with, but I figure looking at the outside of a metal box wouldn't really tell me much more anyway.

So, based on the description, am I correct in assuming that the power supply is most likely kaput?  From what a quick search has told me, pretty much any standard ATX power supply should be able to fit in the case (unlike my own crappy clamshell case), so a recommendation on a good replacement would be much appreciated too.  Keep in mind that the machine in question is pretty much never used for anything system-intensive, so I wouldn't exactly need a beefy replacement PSU, just something basic.

[Mongoose]

Thanks to the people on IRC who listened to me ramble about this today.  (30 views and I can't even get an "I dunno"?  Help a brotha out, guys.  )  At least now I know what I'm looking for.  My easiest option would probably be to just use the PSU Stealth sent me, but there's that issue of the connectors.  From doing some Wiki reading, the four-hole connectors I mentioned are apparently standard Molex, and the cable they're on attaches to the PSU via this six-prong plug.  The problem is that the drives in my family's computer use SATA power connectors, and the cable they were attached to is hard-wired to the old PSU.  I looked on Newegg and found these molex-to-SATA splitters that would presumably work, but is there a similar sort of cable I could get that would go straight from the PSU to a SATA connector?  That would seem like a far less messy option.

[CommanderDJ]

I dunno.

Spoiler:

You asked for it.

[Mongoose]

Guess I did.

Edit: In any case, poking around suggests that those sorts of cables are normally included with PSUs and seem to be difficult to find sold on their own, so maybe I'll just go with the molex-to-SATA adapters.  Hopefully a local tech place around here has them, so I don't have to wait for shipping.

[newman]

If you're getting LEDs on the motherboard to light up then the PSU is actually delivering power to the board. For now I'd eliminate any hardware PSU failures as a cause. Even if some connector wasn't plugged in and the board wasn't getting enough power you should be getting some warning beeps. It could actually be something mundane such as a power switch of your case not delivering the "power on" message to the board somehow; maybe it's pcb died or there's contact loose somewhere or something. Try visually inspecting the wires that go from your power switch to the board. Check the wires themselves and check the pins on the motherboard where it connects. Blow dust from the connector, reconnect, try again. I'll admit it's a long shot but speaking from personal experience when your PSU dies your motherboard won't be getting any power so it's probably not a power cable gone loose issue either. If not all connectors are plugged in so the board isn't getting enough power you won't get any LEDs light up on it either. This is why I think your PSU may actually be fine.

[Mongoose]

Hmm...that's an interesting point.  I wondered about the power switch itself at one point, but since hooking up the other PSU got the system to boot, I figured that it probably wasn't the issue.  Who knows, though.  I'll go back in tomorrow and do a more thorough inspection of the cables.

[newman]

Well if the other PSU solved your problem then it can really be one of two things;

1) Your old PSU died. I'm somewhat skeptical of this because like I said before, your motherboard LEDs shouldn't have lit up at all. I guess it's possible it died in such a weird way it delivers enough juice to get the LEDs working but not to boot anything. But that should have gotten you as far as BIOS or at least get some warning beeps out of it. Something. It's weird.
2) Some cable wasn't connected properly/got damaged. Swapping out the PSU also meant replacing/reconnecting the faulty cable so it fixed the issue.

Depending on the brand some PSUs come with pretty long warranties. What I'd do in your shoes is check if yours is still under warranty and RMA it if that's the case.

[Tyrian]

I just saw this and my electrical engineering major compels me to answer. 

Your PSU is definitely dead.  My advice would be to buy some of those Molex-to-SATA power connectors and test with Stealth's supply.  These should be fine:  Link.  Rosewill usually makes decent utility items. 

What I'd guess happened is this:  When you put a load (anything that consumes power) on the supply, you usually see an effect called pull-down.  Basically, the voltage drops at the supply output.  The net result is that parts in the system are undervolted, and won't run properly.  The supply has a compensator that kicks the voltage back up to normal levels, but if it's blown, you usually see behavior like this.

Bottom line, I think your supply is pushing current, just not enough to power your system.

[Mongoose]

Thanks a lot. That definitely fits with what I'm seeing today...all of the wires and connections are snug and look good, but the same old non-response.  I'll poke around a local place or two today to see if they carry connectors like that, to avoid waiting on shipping if I can, but otherwise I'll go with those.  My mom already needs to get some important file or other off that machine, and I'd rather not go through the trouble of connecting the HDD to my own system if I don't have to.

[Admiral LSD]

Yeah, a PC power supply is really about 5-6 different power supplies in one, each delivering a different voltage (multiple +12V rails, +3.3V, +5V, +5VSB, etc). Seeing lights on the mobo just means the standby power is working, it says nothing as to the status of any of the other rails or the mechanism by which they start up. I've seen similar systems in a bunch of machines recently and it's almost always cleared up with a PSU replacement. The other cases have usually had motherboard involvement, but that's unlikely in your case as you've said it works with a new PSU.

As for Molex to SATA adaptors, you can pick those up just about anywhere. You miss out on the features of the SATA power connector that enable hot plug and staggered startup, but they aren't of much use in a typical desktop environment anyway.

[Mongoose]

Yeah, I don't think we'd ever need any advanced features like that.  I wound up ordering two of the adapters that Tyrian linked, and they should hopefully arrive in the next day or two, so I can finally get the thing up and running.  I probably won't win any prizes for cable management when it's all said and done, but at least it'll work.

Oh, and I did wind up having to connect the HDD of the family system to my own machine, just to get my mom's e-mail inbox for bill-paying purposes.  I was also curious about what sort of connections and such that my system has, since I hadn't really known about any of this stuff until learning it now.  It turns out that motherboard size wouldn't be the only issue if I ever attempted to move this system into a new case...my motherboard has two SATA ports, one of which is being used by my HDD, but the DVD drive and front USB ports are connected by some big ol' PATA cables.  Nothing like old technology, I guess.