My computer won't power on, now what?

One day I came home from an extended time away and tried to turn on my desktop computer. Nothing happened. I tried a new power cord. Nothing. I bought a new power source and installed it, and still nothing. The only thing on that system that appeared to show signs of life was one of the little l.e.d.s in the front - it glowed green. Otherwise the computer was as good as dead, no fans, no disk drive starting up, no nothing.

I’ve had tech experience but I’ve never encountered this situation before. Usually there are signs of power running through the system in various places unless the power source is bad. Since I tried a brand new power source and it still didn’t work, what could it be? I can’t spend a lot of money on this system because it only cost me a few hundred dollars in the first place.

It’s more than 2 years old, so out of warranty. I haven’t used it a lot, and don’t feel I’ve gotten my money’s worth out of it, so I don’t want to give up right away and get a new computer; not to mention that I can’t afford it right now. Any advice about troubleshooting to find the problem? How do I tell for sure if the system board is completely trashed, or if it is some other problem? Are there any other tests I could try?

I think you have about a 95 percent chance of a dead motherboard at this point.

In the old days, all the power supply needed to turn on was power. Now it needs a signal from the motherboard. If there’s a fault somewhere, usually you’ll get a brief flash for a second or so then everything shuts down. If you aren’t getting anything, and you’ve got a new power supply, then either the motherboard is dead, or you missed something hooking the new power supply up (like the power connector for the core voltage on a P4 processor, or the connector for the power switch).

To troubleshoot your power supply (supplies) set them up away from any computer hardware, out of the case. Plug them in; if there’s a switch on the back, turn it ON. Bend a paperclip into a hairpin shape and stick it into the plug to connect the green wire (PWR-ON) to any of the black wires (GND). When you press the power button, the motherboard closes this circuit (grounds the green wire) to “ask” the PSU for power. If the power supply powers up, then you know it’s working for sure. Some power supplies are very quiet – look through the grille on the back of the power supply for a fan; it should spin when power is applied.

If your power supply is fine, you’ll need to check the motherboard carefully. Remove it from the case. Disconnect any peripherals from it, including all hard drives, leaving only minimal input and output (keyboard and monitor). Remove all but one stick of RAM, and put this RAM in the #1 slot. Set the motherboard on a known insulator like a large sheet of cardboard, connect it to the power supply, and using the motherboard manual, reconnect the squid-like tangle of wires from the case (PWR-ON, RESET, PWR-LED, HDD-LED, and so on). You should have a very ugly-looking but sparse setup now:

  • motherboard (on piece of newspaper or cardboard w/ only one stick of RAM)
  • power supply
  • connections to power switches
  • monitor
  • keyboard

Power up the machine. If the machine does power up in this stripped-down state, begin adding components back to it one at a time. As long as you continue adding only one device at a time, the offending device will make itself known. If the offending device doesn’t make itself known, you may have a short somewhere; this is why the motherboard is on cardboard for now. Place it back in the case with a few sheets of printer paper between the back of the motherboard and the case to prevent those pins from touching that inviting conductive metal.

If nothing happens when you power up the machine, replace the RAM in the motherboard with RAM that you pulled. Try again. If nothing continues to happen, it’s likely you’ve got a dead motherboard (the odds of several sticks of RAM all going bad simultaneously are very low). If you can find one, swap in a known-good CPU, and hope that the CPU revives your machine. If you’re desperate, swap your CPU into a friend’s known-good motherboard to verify that the CPU is still alive. If you can’t definitely rule out the CPU as the cause of your troubles, you should assume that both the CPU and motherboard are goners and begin searching for replacement gear. :frowning: If budget is an issue, consider going to NewEgg and getting the same model motherboard. If the new motherboard works with your old CPU, you’re good to go; if not, NewEgg’s RMA process is amazingly friendly. They’re a little more prickly about high-cost, low-margin items like CPUs, so don’t order one until you know you’re going to need it.

I agree, most likely a dead motherboard. But here’s the kicker, you quite possibly have a dead power supply as well. I have seen the following situation occur enough times that I just assume it now:

The power supply goes bad. Because it is bad, it fries the motherboard. You replace the power supply. The computer still doesn’t start, because the motherboard is bad. And by the way, the bad motherboard has now fried your brand new power supply.

You replace the motherboard, but the computer *still *doesn’t start, because the power supply is bad. So you replace the power supply (again), but the last power supply had already ruined your new motherboard.

Repeat, ad infinitum, or until you replace **both **the power supply and the motherboard at the same time.

This may or may not be the case in your situation, but I can tell you from personal experince how frustrating it can be. If your budget allows it, I would recommend replacing the motherboard and buying another power supply, just in case.

Wow, thanks for all the advice. It’s just what I was looking for.

Are you sure that paper clip trick is safe? I don’t have the power supply in front of me but I’ll have to check this out. I’m sure you meant that I should make the paper clip connection before turning on the power supply. Or, waitasec, the plug is probably DC so it wouldn’t matter…right?

I still make it a habit not to touch anything that I know has live current in it. Too easy to make a mistake.

Then, don’t do it. If you’re nervous and afraid you’ll make a mistake, you probably will. But, if you feel comfortable doing so, it’s safe–the signal in question is low-voltage and low-current. With a caveat: don’t run the PSU for long in this state. A switching power supply needs a load of some sort to regulate properly.

Jurph offered a good troubleshooting process. The only thing I might add is just yank everything from the motherboard and only leave the power supply cable, your LED and switch jumpers and CPU (only because they can be a bitch to take off and put on an installed motherboard).

Pull the video card, drives, and everything else.

Try to power on the computer. If the board is good it should complain about not having memory - you’ll heard a series of beeps. If you hear nothing then you know it is an issue with the motherboard, power supply and sometimes a CPU. A dead CPU can cause a board to not post or beep. It all depends on the make of the motherboard.

Opps. Posted too quick.

When I troubleshoot a computer with the problems you’re having, I yank everything and try a power up BEFORE I start tearing the computer apart. I don’t like to pull boards and power supplies if I don’t need to.

It is safe. If it makes you feel safer, you can wear wool mittens or a double layer of latex gloves to ensure that you’re not conducting any current. I’ve done the green-to-black trick several times myself, and was terrified the first time I tried it. It works, it’s safe, but you’d probably be most comfortable watching someone else do it the first time. Like QED said, just ground the green pin for long enough to verify that the fan’s moving.

If it eases your mind any, look at this pinout for an ATX power supply, and an ATX power supply design guide (PDF). Once you’ve skimmed them it will be clear how little power you’re messing with on the PS_ON and GND rails. Like QED said, though, if it makes you too nervous, just skip that step. Nervous do-it-yourselfers and angry do-it-yourselfers can wreck a PC almost as fast as a lightning storm.