Computer Start-Up: Explaination Of How The


The computer start-up process can be divided into three basic steps: Power On Self Test, BIOS, and Boot (or Bootstrap).

Troubleshooting system start-up problems can involve looking at one or more of these steps.

Although many things can go wrong with a computer, perhaps the most frustrating is when your computer won't start at all. This is true, in part, because when your computer fails to start you can not use diagnostic tools to help you determine the problem.

If your computer won't start at all, the power light does not come on and the cooling fan is not running:

Check if the wall outlet you are using will it run another appliance such as a small lamp. Change the wall outlet you are using -- perhaps there is inadequate voltage.

Check to make sure that the computer's electrical cord is securely plugged in at both ends. Switch it with another cord if you have one available to you.

If none of these steps help, it is likely your power supply has gone bad. Power supplies are potentially dangerous units and a professional should replace your power supply if you need a new one. Never open up a power supply box.

Having a bad power supply can be the cause of many problems that may not initially point to that component. For example, spontaneous reboots or freezes and even memory parity errors can be traced to faulty or inadequate power supplies.

It is almost always easier, and often cheaper, to replace a defective power supply rather than repair it.
If you do have to replace your power supply, be mindful of the physical requirements (shape, location, screw-hole positions and so on).

If there is no power light, but your cooling fan is running:

Open up your computer and make sure that your 6-pin power supply cables (there are two) are securely attached to the motherboard (note that such 6-pin cables are unique to your system's power supply harness).

If none of these steps help, you likely need a new power supply.

If your power light is on and your cooling fan is running, but there is no computer activity (you hear no beeps at start-up):

Open your computer and make sure your power supply cables are securely attached to the motherboard.

Examine your motherboard for metal pieces that might be touching other metal pieces (such as screws or the motherboard's seatings). These could be shorting out your motherboard.

Check the seating on all the other expansion boards in your computer. An expansion board that is not seated securely can cause a short.

Make sure all other cables inside your computer are securely seated and in good condition. Look for frayed or crimped edges.

Check that your CPU is inserted properly in its socket, that it is cool, that the CPU heat-sink/fan works and that it is fitted correctly.

If your CPU has a tension lever, make sure it is closed and locked.

If you hear two or more beeps at start-up, but there is no video:

Open your computer and make sure your video board is seated properly it its expansion slot.

Power On Self Test

The Power On Self Test (POST) is the first set of instructions executed during the start-up of your computer. You can recognize it during the RAM test, which is one of the system components that the POST checks, along with the oher key components on the motherboard. The POST order of execution looks like the following:

BIOS

Information about the graphics adapter

Information about the BIOS (name, version)

Information about the RAM (counted)

If the POST detects an error or errors in the system, it will write the error messages on the screen. However, if the monitor is not ready, or if there are video card errors, it provides an audible code. If a catastrophic fault has been detected in the Power On Self Test that your computer does at start-up, the number of these audible beeps can be indicative of the type of failure.

These beeps (or beep code) can be useful in troubleshooting problems prior to the initialization of your computer's video system. The number of beeps is dependent on your computer's particular BIOS and is unfortunately not standardized across manufacturers. If you can match your beep code to your particular BIOS and version, you can accurately diagnose problems with your CPU, RAM, motherboard, video board, or drive controller.

Your system's beep codes should be in the written documentation for your motherboard, or obtainable from the manufacturer's web site.

The following is an example of beep codes from American Megatrends: 1s (short) System RAM refresh failure

2s Memory parity error

3s Base 64-kbytes memory failure

4s System timer failure

5s CPU failure

6s Keyboard controller Gate A20 failure

7s Virtual mode exception error

8s Display memory read/write error

9s ROM BIOS checksum error

10s CMOS shutdown register read/write error

11s Cache memory error

1l (long) - 3s Memory test failure (non fatal)

1l - 8s Display test failure (non fatal)

Your system documentation or the manufacturer's web site may include recommended solutions to these error codes. For example, from American Megatrends:

For 1-, 2-, and 3-beep errors try reseating the system's memory modules. If that fails, it is possible that 1 or more memory modules are bad.

For a 6-beep error, try substituting a different keyboard, or reseating the keyboard controller chip. For an 8-beep error, try reseating your video card or a different video card (if your system has a separate video card).

For 4-, 5-, 7-, 9-, and 10-beep errors, it is likely that you will need to have your motherboard repaired or replaced.

CMOS Setup

The CMOS RAM chip maintains a small amount of information that is essential for your computer to start-up properly. This information includes data about your floppy drive and hard disks, your keyboard, your CPU, cache, boot sequence and much more. These data have to be set up correctly in order for your computer to operate properly. In modern systems much of this set-up is automatic, but occasionally you may need to manually configure your CMOS Setup. In general, you should leave these settings alone unless you are familiar with what you are doing, or you have no other choice.

Keep track of any changes you make to your CMOS Setup settings. Because your CMOS settings are dependent upon your computer's battery, it is useful to make a hard copy (write them down). This way, in the event that your battery fails, you have a backup copy.

If your video works but you see a message indicating a setup problem, you will need to enter into your CMOS Setup in order to look for differences in your CMOS system parameters and your hardware configuration.

How you enter your Setup routine will be dependent on your BIOS manufacturer -- for example, American Megatrends' CMOS Setup is entered by pressing the delete key during the POST. Your system documentation will tell you how your particular CMOS Setup can be entered.

Once you are in CMOS Setup:

Carefully check each entry and make sure that they are reflective of your actual hardware configuration -- in particular check that installed memory and drive parameters are correct. Some parameters, such as ones for the hard disk are usually automatically set on modern system, however, you may need to enable the drive in CMOS Setup in order to have the system recognize it. Make sure your CMOS battery is good by examining your setup parameters, shutting down and turning off your computer for ten minutes, then going into Setup again. If your CMOS is not retaining changes, you will need to replace the battery. Many modern systems will display a warning at start up that the CMOS battery is getting low.

If changes you make to your CMOS Setup are not saved after rebooting:

Check to make sure that you are exiting the CMOS routine properly. Often the default exit will not include a "Save." Video Problems

If your computer appears to be starting normally but you see no video activity:

Make sure your monitor is plugged in and turned on.

Make sure your monitor is working by trying it on a known, good, working system.

Make sure your monitor's cable is securely seated in the video board slot.

Make sure your video card is securely seated in its expansion slot.

Try a known, good, monitor. If it does not work, you may need to replace your video card.
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