WARNING: NEVER PLACE ANY COMPUTER COMPONENT ON A METAL SURFACE! I sadly repeat an error in this video where I place computer components on the metal chassis of my computer case: THIS IS AN ERROR ON MY PART! PLACE THE COMPONENT EITHER ON A NON-CONDUCTIVE SURFACE SUCH AS WOOD OR NON-SHINY CARDBOARD, OR PLACE THE COMPONENT IN AN ESD-SAFE ANTI-STATIC PACKAGING WHEN NOT INSTALLED IN YOUR SYSTEM.

WARNING - I will NOT be held responsible for any damages the methods shown in this video may cause to yours or someone else's computer, hardware, software, and/or data, including loss of use of such devices and/or loss of data and/or loss of profits from the resulting inability to use such devices and data. Any information or program you choose to put into use from this video is done AT YOUR OWN RISK. As a precaution, I recommend backing up any irrecoverable data before practicing any of the methods shown in this video.

This video will show you how to possibly fix a desktop PC that, when powered up, the lights turn on, the fans spin, but NO image or text appears on the screen and NO POST beep error / message codes can be heard (essentially, the computer does not enter POST and does not boot the OS).

Typically, the CMOS (the component that governs which components are connected to your motherboard and how they interoperate between each other) has become confused and needs to be cleared AND / OR two or more incompatible components are present and have developed a conflict with one another and have to be switched or replaced AND / OR one or more components have gone bad (become faulty) and have to be replaced.
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Do what the video shows: Disconnect the power cable, remove the CMOS battery, short the CMOS jumper pins for 9 seconds then return the jumper cap to its initial position (only if you can find these jumper pins; if not, skip this step), press your PC's chassis power button switch (to discharge any remaining power circulating in the system), leave the PC unplugged and in this state overnight, then the next day return the CMOS battery to its socket, power up the PC, and if no beep, then disconnect the power cable, press your PC's chassis power button switch (to discharge any remaining power circulating in the system), remove one component, power up the PC, and if no beep then repeat (each time unplugging the PC, pressing the power switch to discharge remaining power, removing a remaining component, and then powering up, and this until the PC beeps at boot).If it never beeps, even when you are down to just motherboard, power supply & CPU+fan, one of these remaining components may be bad
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Beep error codes differ from one BIOS manufacturer to the next. To discover what the beep error code is trying to telling you, discover the manufacturer of your BIOS (available in the motherboard's manual or on the motherboard's manufacturer's website {on the page for your specific motherboard model}) and then look up the frequency and interval of your beep error code on:

http://www.computerhope.com/beep.htm
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If this is new hardware that you are installing on your motherboard (that has not yet functioned on your motherboard), note that matching bus types of video card to motherboard socket (PCI-E for example), matching socket types of CPU to motherboard socket (LGA1366 for example) or matching bus types of RAM module to motherboard socket (DDR3 for example) does not necessarily signify compatibility. If this is the first time you are trying this hardware on your motherboard, there is a chance that this new hardware is not compatible with your motherboard, despite the same bus type and despite the fact that the new parts fit in their respective motherboard socket. Your motherboard manufacturer's website will have a support page dedicated to your motherboard's model, and on this support page should be a compatibility list for such components as video cards, CPUs and RAM modules. Ensure that your new component is certified to function with your motherboard, and if your new component is not present on the compatibility list, then there is a chance that the new component is not compatible with your motherboard.
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If your computer powers on but for a mere second or two and then immediately powers down, It sounds like your motherboard is developing a short circuit due to contact with the metal casing. Most likely it has to do with the screws and metal mounting stands (supports) that your motherboard sits on. The cheapest way to fix this problem is to introduce cardboard washers between the screws and where they make contact to the motherboard, or you can buy plastic mounting supports at a computer shop.

Alternatively, you can always Breadboard it (explained in the following video:)

If the steps in this video did not provide a solution to your problem, view:

   • Advanced troubleshooting technique tu...  

You never know, maybe rebuilding the PC in the opposite sense that you took it apart will solve the problem.