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Section 2: POST

Background:
"Power-on self-test is the common term for the pre-boot sequence of a computer, a router, or a printer. The same basic sequence is present on all computer architectures."[source] During the POST, the BIOS detects the hardware configuration of the system, and runs basic tests on the various interfaces. The exact nature of these tests varies between BIOS manufacturers. After the completion of the POST test, the BIOS transfers control to the boot loader. Next, the boot loader transfers control to the Operating System.

Important!
If your computer is powering on, but is not displaying anything on the screen or is making a strange series of beeps after you turn it on, but does seem to power on and you have tested the power supply for any issues; this is where you should begin your troubleshooting.

If you are getting a "random" series of beeps, your first step should be to identify the BIOS that is installed in your system. You can usually find this information one of two ways. The easiest would be to find your motherboard model, and look it up in the manufacturer's information. Look in the appendix for links to manufacturer websites. The second, and often more difficult way, is to open the case of your computer and attempt to locate the BIOS chip itself, and use the information on the chip to identify the manufacturer. Once you have identified the manufacturer, you can use the resources below to better understand the nature of the error code.

General POST troubleshooting. This section helps diagnose general problems with a system that refuses to POST.

  1. Remove any and all hardware from the computer with the possible exception of the processor (if you feel comfortable removing your processor and have the tools and equipment required to reseat and reattach the thermal system). You should also remove the silver CMOS battery, if possible for a few seconds and then replace it.
  2. Use compressed air to clean the dust out of the machine at this time. Pay particular attention to the RAM, PCI, and AGP slots on the board. Dust in these slots can cause the card to get a poor connection and consequently, the POST to fail. Do not use a vacuum to clean during this process. Household vacuum cleaners build up a heavy static charge while they operate. An accidental static discharge from a household vacuum could easily destroy one or more important pieces of hardware. You have been warned.
  3. Reinstall the following pieces of hardware:
    • Processor and thermal system (if removed before)
    • 1 stick of RAM (only one, and put it in the RAM slot closest to the processor)
    • Video card (iff your motherboard does not feature on-board graphics)
    • Reconnect the power supply to the motherboard only, with the possible exception of those graphics cards that require external power from the power supply.
  4. Go over each piece of hardware that you just installed, make sure that each piece is firmly "clicked" into place and is not loose. Attempt to power the computer up.
    • If the computer displayed something on the screen, turn the computer off. Begin a process of elimination to determine which piece of your hardware was causing the POST to fail, by powering the system down, adding back one piece of hardware, and powering the system on.
      • If you determine that one particular piece of hardware causes the POST to fail, then you have located your faulty hardware. Replace the faulty hardware. Go to the System Diagnostics section.
      • If you are unable to so locate a piece of hardware, it is possible that a piece of hardware was simply loose, and the act of reassembling the system cleared that up. Go to the System Diagnostics section.
    • If the computer still did not boot properly, or display anything on the screen, you may have a defective motherboard, processor, video card, or stick of ram. Take your system to your local computer shop and have them look at it to see if they can determine which of your parts is defective. A good repair shop should not charge in excess of about $70 for this service. If you have known-good parts that are compatible with your system, feel free to attempt to use them to isolate the failed piece of hardware. Try using a different stick of ram or a different video card. At this point, you should look again at the motherboard, attempting to locate any leaky capacitors or cracked traces. Go to the Power System section for further information about this.

If you have just attempted to flash your BIOS, you may be suffering from what is called a "bad flash". This is a condition where the BIOS is corrupted, and is unable to function properly. This can result from a number of situations: powering down the system during a BIOS flash, flashing the BIOS with the wrong update, or a faulty bios chip. The first two situations are nearly always recoverable, so long as the manufacturer of your BIOS is either AMI or AWARD. The procedure for recovering from a corrupted BIOS for these BIOS manufacturers is covered on http://www.biosman.com/biosrecovery.html . If you are unable to recover using those methods, or your BIOS manufacturer is not AMI or AWARD, you should contact a reputable BIOS dealer (as linked above) to purchase a replacement BIOS for your motherboard.

Resources
Sources for information about BIOS beep codes:

Proceed to next section: 3. System Diagnostics