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POST - Power-on Self Test
When you first turn on a computer, it runs what is called a POST, or power-on self test. This is a quick diagnostic utility that makes sure your computer has what it needs to run, and it loads before the operating system (such as Windows) even starts up. The purpose of the POST is to let you diagnose any hardware issues before trying to load software from a hard drive. If you turn on your computer and get no POST at all, it could indicate a serious problem.
No POST typically means there is an issue related to the motherboard. Maybe you've got the RAM installed incorrectly or a bad piece of hardware is causing a conflict that keeps the system from working. Perhaps your power supply is malfunctioning and not providing enough juice to turn on the equipment. It could also mean your motherboard has died and will need to be replaced. In this article, we'll run down the things you can test before you have to buy any replacement parts.
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Reseat the RAM
The quickest and easiest test you can do is to unplug the RAM from the slots on the motherboard, then plug them back in. If you have two or more sticks of memory, swap them between the slots that they use. After reseating the RAM, turn the computer back on and see if it works. I’ve found this trick works well with some of the HP business desktops we use at my work. You may also want to try the RAM sticks one at a time to see if perhaps one of them has gone bad.
(Image credit: Motherboards.org)
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Check the Monitor Connection
If you turn on your computer and get nothing but a blank screen, it could just be that your monitor is not hooked up correctly. If you are using an extra video card, make sure you have the video cable plugged into that card and not the connection on the motherboard. With most computers, the onboard video is automatically disabled when a new video card is installed in the PCI Express or AGP slot.
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Swap the Power Supply
Not everyone has a spare power supply laying around, but if you do then try swapping it out and see if it makes a difference. If your motherboard is not getting a POST or even when the computer won't turn on, it could be a problem with the power supply and not the motherboard. I've seen computers behave exactly the same way with a bad motherboard as they do with a bad power supply when you press the power button.
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Look for Bad Capacitors
Visually inspect your motherboard for leaky or puffed out capacitors. These are the little cylindrical things that stick up all over the motherboard. They should have a cross-like pattern on top, and the top should be flat. If you see any that are puffed out or leaking a white or yellowish fluid, then it means that capacitor is either blown or going out. Either way, you’re going to need a new motherboard. Don’t even think about trying to solder a new one in place.
(Image credit: Hardware-one.com)
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Minimize the Hardware
When diagnosing motherboard problems, it always helps to minimize the number of contributing factors. If you get no POST when pressing the power button, try disconnecting all your drives and remove any cards from the expansion slots so that you are running the computer as barebones as possible. I once had a bad modem with a tiny melted diode that caused the entire computer not to POST. When I took that modem out of the PCI slot, everything worked fine.
If you unhook all your hardware and are finally able to POST, you should then turn off the computer and add back your drives and expansion cards one at a time until you figure out which one is actually making trouble. If you are using a high end video card, such as for gaming, you need to make sure your power supply can handle it. Most of them require a 350 watt or higher power supply and your computer will not function correctly if it is underpowered.
For more information, check out my article on what to do if your motherboard keeps rebooting.