How to Troubleshoot a Computer That Will Not Power On


A computer that will not power up can be diagnosed by following a straightforward plan of action. Once the obvious reasons are eliminated, the next step is to remove all components that are not crucial to the system to reduce the load being placed on the power supply. If the computer still will not boot the process of parts swapping is begun.

Things You'll Need

  • Power supply
  • Voltage meter
  • Phillips-head screwdriver

Eliminate The Obvious

  • Check to ensure that the electrical cord is plugged into the wall socket as well as being firmly plugged into the back of the computer .

  • Verify that the wall socket is live by using a voltage meter, or alternatively, a lamp.

  • Ensure that the rocker switch mounted on the power supply on the back of the computer is in the "on" position.

Individual Components

  • Open the computer case. In many cases you can remove the side panel by removing the screws that secure it to the computer chassis. This procedure may vary from computer to computer.

  • Remove the power and data connections from the CD/DVD drives and from all hard drives.

  • Press the front power switch and attempt to power up the system. If the system powers up, this indicates that the power supply does not have a high enough load capacity to power the computer's components or that it has suffered a failure that has reduced its capacity. In either case the unit needs to be replaced .

  • Replace the power supply with a new higher-capacity power supply or a good used unit, reconnect the CD/DVD and hard drives and attempt to power up the system. If the computer powers up, shut it down and reinsert each of the add-on cards one at a time and retest the computer as each component is added. This will identify which card or cards caused the failure. If the computer does not power up after you replace the power supply, the problem is obviously elsewhere.

  • Unplug the drives, pull out all of the add-on cards and attempt to power up the system, leaving in the newly replaced power supply. If it powers up, you can continue the troubleshooting process.

Motherboard, CPU and RAM

  • Remove the RAM and replace it with either brand new RAM or known good parts.

  • Test the system by attempting to power it up. If the RAM replacement allowed the system to power on, shut down the system, reinsert all the add-on cards, plug in the drives, and retest the system.

  • Replace the motherboard and CPU (central processing unit or the main processor) if the RAM replacement did not solve the problems. Use the original RAM from the system and check to see if the system powers up. If the system powers up, you are ready to start adding the old components back into the system.

  • Reassemble the system using all of the original parts and ensure that the system is functioning properly by running it overnight using a software package that causes the computer to stay busy.

  • Verify that the part determined to have caused the failure is really bad by installing it in another system and seeing if it forces a failure in that unit as well.

Tips & Warnings

  • Never swap out more than one part at a time with the exception of the CPU and the motherboard on which it is mounted. CPU and motherboard replacement need to be evaluated on a case-by-case basis. In older systems the cost to replace these components may equal or exceed the cost of a new computer.
  • Never remove or replace a part while the computer is powered up.

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