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Why doesn't my computer power up?


My computer will not boot up at all. It will not turn on when I push the button. I think it is the power supply.

Is there anything else it could be?


This question was answered on February 9, 2002. Much of the information contained herein may have changed since posting.


This problem could be from the power supply, it also could be from the switch on the power supply inadvertently being flipped or even a failure of the power cord I would first check to make sure that the power supply switch on the back of your tower did not accidentally get flipped Next I would try a different power cord, and then try replacing the power supply

Before you go shopping for a new power supply, find out what type of power supply is in your machine There are two main styles, AT and ATX The older AT style is usually found in first generation Pentium and older AMD machines If your machine is less than 3 years old, it most likely has an ATX style power supply The main difference between the two is in how they connect to the motherboard The AT style has two identical looking 6-wire connectors, usually labeled P8 and P9 that plug right next to each other into a special connector on the motherboard The ATX style has one 20-wire connector The easiest way to find out what you need is to take the cover off your computer and look at the power supply It usually has a sticker on it that documents the type and power.For example, it might say something like AT-250W, indicating it's an AT style 250 Watt, or ATX-300W,indicating it's an ATX style 300 Watt power supply As computers get faster, have more room for expansion, and hardware requiring more power, it's important to buy a strong, good quality power supply A 300W should be the minimum these days If you plan to replace the power supply in an AMD Athlon system, you should first consult the AMD web site at

to find out what models are approved.

Replacing the power supply can be relatively easy and safe if done correctly First shut down your machine, unplug the power cord, and take the cover off the case Disconnect all the power cords from the

drives and the motherboard Then remove the power supply itself Look at the back of the case There are four screws around the power supply, on the outside of the cutout for the power supply Remove the screws, but be sure to grab the power supply with one hand and hold it in place when removing the last screw so it doesn't drop into the case and damages any components Carefully lift it out

Before you install the new power supply, take a look at the back of it There should be a red switch right underneath the plug for the power chord Be sure that this switch is set to the correct voltage For example, if you live in the U.S it should be set to 115V Most of the time they are set correctly by default, but you don't want to take any chances, so take the extra second and check to be safe.

Now carefully insert the power supply into the case and position it in the proper position You'll notice that the cutout for it is shaped so that it only fits a certain way Screw it in securely Then look at the bundle of cables coming from the power supply Figure out which string has what type of connectors on it and reconnect them to your devices and motherboard.

If you're installing an AT-style power supply, you'll notice that there is an extra cable that hasn't been mentioned yet It is for the power switch One of the differences between AT and ATX is that with

AT-style cases the power button connects directly to the power supply to turn the power on and off On ATX-style cases the power button connects to the motherboard instead The replacement AT-style power supply probably came with not only the cable to the power switch, but

also had a new power switch attached to it This will leave you with two choices:

Use the new switch - This means you have to remove the old switch and install the new one instead.

Use the old switch - This means you leave the old switch in the case If you look at the switch from inside the case, you'll notice that it has four different colored wires that run to the power supply.

Carefully write down what color wire connects to what pin, then simply pull the wires off each pin.

After installing the new power supply, remove the new switch it came with and plug the four wires onto the pins of the original switch following the color coding you wrote down earlier,

unless you have reason to suspect that the old front power switch is bad and needs replacing Using the old switch is a lot easier, and doesn't require removal of the front bezel, trying to screw tiny screws into even tinier plastic holes at impossible angles

At this point your done, replace the cover and plug in you power cord and you should be good to go

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Posted by Becky of Chandler-Gilbert Community College on February 9, 2002