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Troubleshooting a Dead Computer
By Stephen Bucaro
The Windows startup sequence is nightmarish, bloated, overcomplicated mess. If you fully understood it,
you would think it a miracle that Windows starts at all. If you have ever experienced your computer
freeze up part way through the startup sequence, or beep and spew out error messages rather than
starting up, you may think your computer is dead for good. But understanding the Windows startup sequence
can help you to diagnose the problem and bring it back to life.
Power-on Self-Test
When you first turn your computer on, it has no intelligence at all. It doesn't know how to read
a floppy disk or hard disk. The computer uses a small program stored in a read-only memory (ROM) chip call
the Basic Input Output System (BIOS) on the motherboard to load the operating system. But first the BIOS
performs a Power-on Self-test (POST) to check the computers major hardware components.
The first step in the POST is to hold the CPU (Central Processing Unit) in reset until the power supply
sends the "Power Good" signal. If you have an improperly installed expansion card or cable, or if a
component has failed, it may overload of the power supply preventing the Power Good signal. The power
supply itself may have failed.
If the Power Good signal is received, the CPU comes out of reset and begins executing POST routines in
the BIOS to check the computers RAM (Random Access Memory), keyboard, serial port, parallel port, video
adapter, floppy drive, and hard drive.
The BIOS requires some RAM in order to work, so the first thing POST does is test part of the systems RAM.
If that test fails, your computer won't boot. To troubleshoot when your computer stops this early in the
boot process, remove all RAM chips and install a known good chip in lowest bank of RAM.
Until the video driver is loaded, the only means of communication the computer has is a small speaker
inside the computer to send beep codes. For example, it may emit three beeps if it finds a bad memory
chip, six beeps if it finds a bad keyboard.
Unfortunately there is no standard for POST beep codes. If your computer is beeping when it tries to start,
you will need to find out exactly which BIOS your motherboard uses and contact the manufacturer for the
meaning of the codes. Most BIOS chips are made by American Megatrends, Inc (AMI).
Many POST routines use a single beep to test the speaker itself or to indicate successful completion of
the POST. If your computer emits only a single beep on startup, you probably don’t have a POST problem.
The situation is complicated by the fact that many expansion boards have BIOS chips that are an extension
of the motherboard BIOS. The motherboard BIOS scans for other BIOS’s on drives and expansion boards.
Some expansion board BIOS chips also emit a single beep when they are initialized.
Most video adapter board BIOS chips contain a character ROM that permits them to display text on the screen
before the video drive is loaded. After the POST sequence has progressed to the point that it has checked
out and initialized the video adapter, it begins communicating by displaying messages on your computer screen.
Unfortunately, sometimes you can't see the POST messages because the computer manufacturer displays a logo
on the screen. If your computer gets stuck with a logo on the screen at startup, try pressing the Escape
key to remove the logo.
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