Pin Me

Why a Computer Unexpectedly Reboots at Startup

written by: John Garger•edited by: M.S. Smith•updated: 5/23/2011

One of the most frustrating computer ailments occurs when a computer continually restarts itself when booting up. This article explores two of the most common causes of unexpected restarts, bad memory and a faulty power supply.

  • slide 1 of 4

    One of the most common computer problems users face occurs when a computer continually restarts during boot up. Sometimes the computer is caught in a startup-reboot cycle that could continue indefinitely if left uninterrupted. The key to solving this problem is to start with the two most common causes of reboots at startup. From there, application of the scientific principle is the quickest method for troubling shooting this problem.

    Computers are complicated machines made up of many parts each made by a different manufacturer. Each of these components must work in concert to produce a reliable computer. Consequently, troubleshooting computer hardware errors is difficult even for seasoned troubleshooters. The best method for diagnosing a computer hardware failure is to change just one thing and see if the problem persists. By trying more than one fix at a time, it will be impossible to say with certainty which fix eliminated the problem. This scientific approach to computer troubleshooting can be more time consuming but much more effective in rooting out the cause of a computer malfunction.

    A computer, like any electrical appliance, can be dangerous because of the inherent dangers of electricity. Even when a computer is turned off and is unplugged, the danger of electric shock is still present. Computers contain many capacitors, especially in the power supply, that can hold powerful charges even when unplugged. Therefore, working inside a computer is best left to a professional technician.

  • slide 2 of 4

    Power Supplies as the Cause of Unexpected Computer Restarts

    Power supplies are probably the most unreliable component in a computer. They supply the only source of power to all other components and can be likened to the circulatory system of the human body: no circulation, no life. If the components do not receive a steady flow of electricity, they will cease to function or function sporadically.

    As mentioned above, capacitors hold an electrical charge to ensure that components downstream receive a steady flow of power. These capacitors are connected to the mainstream of power with solder that can weaken over time. As the solder heats up it expands and can expand so much that it no longer makes a solid connection between the power entering the capacitor and the power exiting the capacitor. When this happens, electrical flow is temporarily cut and the computer’s components no longer receive power. When this happens, the computer interprets the cut power as a shutdown just as if the user had pushed the reset button on the front of the computer. The result is a cycle of shutdowns as the solder expands and shrinks with each restart. Although power supplies may malfunction in other ways, this is one of the most common causes of unexpected computer restarts.

    Unfortunately, there is little a computer user can do to fix this problem other than replacing the power supply unit. Power supplies are not user serviceable and usually carry strict warnings about not opening a power supply. The risk of shock is too great to warrant attempting to fix a power supply so unless you are a licensed electrician with expertise in troubleshooting power units, it is time to buy a new one. Again, if you lack the expertise to open up a computer, it is better left to a trained professional. Your best solution is to check if your power supply is still covered under warranty. If it is, contact the manufacturer and arrange an exchange. Otherwise, the power supply will need to be replaced. If you are uninitiated in computer components, consult with an experienced computer technician concerning the correct wattage and features your new power supply needs to be compatible with your computer.

  • slide 3 of 4

    Memory (RAM) as the Cause of Computer Reboots

    The memory (or RAM) in a computer is a vital component where information is temporarily stored while the computer is processing requests, running programs, conducting diagnostics and other vital functions. Second behind only the power supply, RAM is the most common hardware to go bad in a computer. Memory, with its tiny transistors, is extremely sensitive to static electricity, spikes in power, and shorting out due to improper connection to the mainboard (motherboard). The result can be funny computer behavior including the most common error, constant restarting of the computer.

    When a computer first boots up, it normally runs through a POST or Power On Self-Test. This is the flashing of text that appears when you first turn on your computer, assuming you have the OEM logo disabled in the BIOS. Otherwise, the POST process is not displayed on the screen. During POST the computer checks to see what hardware is attached to the computer. Naturally, this includes the computer’s memory. Often, the POST process will correctly identify the type and amount of RAM installed in the computer even when the RAM is faulty. When the computer reaches the point where the operating system is loading, it starts loading drivers and other necessary code into memory. As the memory fills up and hits the faulty memory area, the computer crashes and a restart is initiated as a result of the crash.

    Often, computers have multiple memory modules or “sticks” of RAM meaning that not all memory modules may be at fault for computer restarts. Unfortunately, faulty memory can only be replaced; they are unserviceable by the user. Most RAM manufacturers offer at least a one-year warranty on their products. If your RAM is still covered under warranty, contact the manufacturer and see if you are eligible for a replacement. More times than not, the manufacturer is helpful in diagnosing and ultimately replacing the RAM if the problem remains unresolved.

  • slide 4 of 4


    The two pieces of hardware that are most commonly the cause of an unexpected restart are the power supply and the memory. These two computer components are notorious for causing this problem and are the first place an experienced troubleshooter looks when diagnosing the rebooting problem. One way to protect yourself against this error is to ensure that these two components especially are covered under a long warranty. Without a warranty, it may be necessary to buy a new component to replace the faulty one. Many advanced computer users who rely heavily on their hardware keep spare power supplies and memory on hand in anticipation of the errors discussed above. Other than having a second computer, this is the only way to ensure that your computing experience will go virtually uninterrupted.