This is a very basic, general guide intended to provide a basic explanation of what happens when a computer powers up and what you should expect to find. It may not help all users but it can get you started troubleshooting your computer by helping to identify which piece of hardware may be defective.
Step 1 - Does It Power Up?
Plug in your computer does the computer show any signs that is is getting power? Press the Power On button does it power up? Take the case cover off are there any lights lit on the motherboard?
If you get no signs that power is getting to your computer at this point it could be many things. It could be the power supply, the motherboard or on some motherboards the memory or the processor. Most modern computers will turn on with the motherboard having just the power supply and maybe some memory plugged into it.
If it doesn't, take a voltmeter and measure the pins in the large connector that plugs into the motherboard. If you don't get any voltages like 3.3 volts or so on one of the pins the power supply may be bad. You will have to substitute a known good power supply to be sure. Even though you may measure 3.3 volts the power supply may still be bad there are many different voltages coming out of it. Step 2 - It Does Power Up But Nothing Else.
Take a voltmeter and measure the pins on the small connectors that plug into the hard drive. You should get +5 volts and +12 volts with the ground connected to the case. If you don't, the power supply is bad.
Disconnect everything from the motherboard except the power supply, the processor, the memory and the video card with a monitor hooked to it. Before you disconnect everything make a drawing of where everything goes. There are wires that go to the switch and lights on the front case, you don't want to remove those.
Press the power on, does it do anything? It should start to boot showing the computer manufacturer's logo or an error message saying "System Disk Not Found", which is fine because in this state there is no system disk. If you get nothing at this point it could be the motherboard, the processor, the memory or the video card. The only way to troubleshoot at this point is substitution.
I realize most people don't have extra processors and memory laying around so you may not be able to complete this step. For people that do have hardware laying around try substituting each piece until you get a changed result. A computer that was hit by lightning or a power surge may have multiple problems and may not react correctly when swapping hardware. In a case like that you may be out of luck in that you won't be able to figure out what is wrong. This tutorial is under the assumption that there is a single problem which is usually the case. Step 3 - It Powers Up, But Won't Boot.
Your motherboard should now have the power supply, processor, memory and video card with a monitor connected. You should get something on the monitor screen that you normally would get except it doesn't complete the process to full boot. Unplug the computer and connect your hard drive to the motherboard. Upon power up you should hear it spinning. If it doesn't spin unplug the computer, disconnect the signal cable but leave the power cable if it still doesn't spin it may be defective. Using a voltmeter measure the voltages on the power connector pins there should be +5v and +12v if not if suspect the power supply.
If your hard drive is connected and you get a "System Disk Not Found" error now that is incorrect. You may have gotten a virus that wiped out you boot sector or damaged the windows boot files. If the Windows files are damaged by a virus it is suggested that you re-install Windows and do a Full Format when it asks you about that. This way no corrupt files will be able to infect your new installation.
If you recently installed new hardware and now it won't boot remove it and see if it will then boot correctly. If it is a pc card try plugging it into another slot, it will get another IRQ and may work because now there is no IRQ conflict.
If it now boots add each piece of hardware one at a time re-booting after each piece. If it hangs or won't boot you will know which piece is causing the problem. If it is a pc card try it in another PCI slot of if that doesn't work forget it or replace it.
We hope this computer repair tutorial and the help and tips enabled you to identify the problem that was keeping your computer from booting.
