They always say there’s no such thing as a stupid question, but maybe they just haven’t heard this one yet. Anyway, my computer has gone from turning on when I hit the power button to doing nothing (and I did check all the cords and whatnot to make sure they were plugged in). I figure that it’s most likely that the power supply died, but I just want to check and make sure that there’s not something else really obvious that I’m overlooking before I go out and buy one.
And as long as I’ve got your attention, the power supply in there right now is 350W. How much do I need to worry about matching that number?
Let’s not overlook the bleedingly obvious. You have plugged something else into the same exact receptacle, and it works, yes? If you’re going through an outlet strip, substitute a known good one, or bypass it, temporarily. Swap a known good power cord for the one in question. No overload resets, in line circuit breakers, or any other protective devices?
You paid the electric bill, and other electric things in the house are working right now, too?
ETA: As long as you purchase a replacement power supply with equal to or greater wattage capacity, you should be fine.
If your 'puter happens to be a G-5 iMac, there’s a power issue under recall. They only tell you about it when it actually breaks. I took mine to the Apple Genius Bar, and they fixed it in about an hour.
An ATX style PC (what most folks have these days) requires a signal from the motherboard to turn on. You’ve got a 50/50 shot of it being the motherboard or power supply. Check for loose connections between the power supply and motherboard, and make sure that the wire for the power switch hasn’t pulled out. If you have a multimeter, you might want to check that the power switch actually switches. Sometimes they break too.
Make sure the new power supply is rated for 350 watts or higher.
Before you buy a new power supply, disconnect all of the disk drives and pull all of the cards out of the motherboard and see if it turns on. It could be something failed short and is forcing an overload condition on the power supply. A lot of times when this is the case, you can see the CPU fan “twitch” when you try to turn on the computer. This is because it momentarily receives a voltage until the power supply’s protective circuitry kicks in and cuts the power.
Also, this is one of those idiot checks, but make sure no one bumped the on/off switch on the power supply itself, if your power supply has one.
It is possible to test an ATX power supply without connecting it to a motherboard. You have to short the PS-ON signal to ground (pins 14 and 15 on the ATX power connector) and the power supply will turn on. If you don’t have a lot of experience playing with electronics and wires, don’t muck around with stuff like this. You can hurt yourself.
They’re around ten dollars and can unambiguously tell you whether the power supply is bad or not. An excellent investment for anyone who ever needs to troubleshoot PCs.
As for the power output, as long as it isn’t lower than 350W, you should be okay. The computer is only going to draw as much power as it needs, so higher power ratings won’t hurt, and may help if you are planning on upgrading any components in the future.
Or you can just use a paper clip. Disconnect the PSU from the rest of the machine but leave it plugged into the outlet. On the 20- or 24-pin motherboard connector, there should be many colored wires; the green one is the important one. Use a paper clip bent into a V to connect the pin at the end of the green wire (PWR ON) to any pin at the end of a black wire (GND) – this simulates pressing the ON button without interference from an actual button or a motherboard in the way. If the fan spins up, you have a working power supply and it’s your motherboard.
Power supply testers can test all of the connectors and each of the necessary voltages, (±5, ±12, +3, etc.). I’ve had bad power supplies that are lacking the proper voltages and cause computer problems even though they have enough power to turn on the fan.
I admit though that in the current situation, with no power to the computer at all, the paper clip trick will work just fine to diagnose the problem.
I had a similar problem and through troubleshooting I was 99.9% positive it was a bad power supply. Bought a new one, put it in, nothing. Turned out the brand new right off the shelf replacement was bad as well.
I guess I pushed the button just right, cause the computer turned on and promptly entered the BIOS so I could tell it all about the new CPU it was seeing. Oh well, at least I hadn’t gone out to buy a new power supply just yet…
(The computer in question is about 5.5 years old. I’ve been thinking for a while that I would need to replace it soon, but I was hoping that soon would be a little later. Thanks everyone for the info.)
Sometimes the stupid button gets stuck partly in, and you have to sort of wiggle it to make it pop out again. Then it will work again for a while. When turning it on, be sure to press it in the middle, straight in.
In that age range, it’s possible you’ve got one or more capacitors going bad on the motherboard.
Read that wiki article, then look at all the capacitors on the motherboard. If you find any leaking or bulging, there’s your problem. The only rational repair is to replace the motherboard.
