Turning the Computer On and Off

Most of us start our desktop computers by pushing the On/Off pushbutton on the front panel. It would appear that the pushbutton is a simple power switch, but there's more to it than that.

Whenever the computer's power supply is connected to AC power (and the master power switch on the back panel is turned on), it sends a +5-volt soft power signal called +5 VSB (or + 5 volts standby) to the motherboard, which is enough to keep some components in a standby condition. On many motherboards, a green LED indicator lights whenever soft power is alive.

When a user pushes the On/Off pushbutton, it's an instruction to the motherboard to send a signal back to the power supply to turn on all of the power supply's other output voltages. After the motherboard receives these additional voltages, the BIOS to begin the startup routine described in Chapter 7.

In many computers, the BIOS offers several additional startup options. When these options are active, the BIOS automatically sends the startup signal to the power supply when the motherboard detects one of these events:

An incoming signal from a network connection
An incoming telephone call through a modem
Any keyboard activity or a specific "hot key" entry from the keyboard
Any motion or pushbutton activity on the mouse

If you discover that your computer appears to mysteriously turn itself on without warning, one of these startup options is almost certainly to blame. To enable or disable these auto-start functions, open the BIOS Settings utility and look for a list of startup or power management options.

Configuring the power button

When the computer is off, pushing the power button on the front panel turns it on. But if you push the same button when the computer is already running Windows XP, the computer will take the action specified by the current setting of the Power Options Properties dialog box. Your choices include:

Do nothing
Ask for instructions
Stand by
Hibernate
Begin the Shut Down routine

If you hold down the power button for more than four seconds, the computer will turn itself off, regardless of what it is doing at the time.

To change the Power Button setting, follow these steps:

From the Windows Control Panel, open the Power Options window.
Choose the Advanced tab to open the dialog box shown in Figure 16.3.

Figure 16.3: Use the Power Buttons options to control the On/Off button.
Open the drop-down menu in the Power Buttons box in the lower half of the dialog box. The options are
- Do Nothing
- Ask Me What to Do
- Stand By: In standby mode, the computer turns off the monitor and hard drives to save power. When you restore from standby by pressing a key or moving the mouse, the computer returns to exactly the same condition it was in before it went into standby.
- Hibernate: When the computer hibernates, it saves a copy of the data currently in memory to a disk, and then it shuts down. When you restore the computer, it reads the data from the disk and returns to the same condition it was in before it went into hibernation.
- Shut Down: When the computer shuts down, it systematically closes all active programs and services, and then turns off the power (except the +5 volt soft power).

The reset pushbutton

The reset pushbutton on the front of your computer is a normally open switch. When you push it, it turns off the computer and starts it up again. This is known as a hard reboot because it immediately shuts down all activity without saving anything and restarts from scratch.

Reset is a last-resort method to shut down or restart the computer when the computer has frozen, or if it has gone into some kind of runaway process and nothing else works. Before you push it, try the Escape key, or press the Ctrl+Alt+Del combination and choose Turn Off or Restart from the Shut Down menu.

Some recent computers don't have separate reset buttons. If yours is one of those, you can turn off the computer by pushing the power button and holding it down for about four seconds. To restart the computer, release the power button and push it again.

Windows shut down

One of the greatest mysteries of the Windows design is the fact that you click the Start button to shut down the system. It must have seemed logical to somebody, so the rest of us have to put up with it. When you have ended your session using Windows and you're ready to turn off the computer, the most common method is to follow these steps:

From the Start menu, select Turn Off Computer at the bottom of the menu.
When the Turn Off Computer window appears, choose Turn Off.

The Turn Off Down command instructs Windows to end things in a systematic manner by closing all the active programs and services and storing all the settings it needs the next time you turn the computer back on. If any active programs have open files, those programs may offer to save the files before Windows closes the program.

Windows has at least three other ways to perform a systematic shut down:

Press the Ctrl+Alt+Delete keys to open either the Task Manager window or the Windows Security window (depending on whether or not the Welcome Screen is active in Control Panel User Accounts Change the way users log on or off).

If you see the Windows Security window, choose Shut Down. If you see the Task Manager, select an option from the Shut Down menu.
Right-click the taskbar which is usually at the bottom of the Windows desktop, select Task Manager from the pop-up menu, and then select an option from the Shut Down menu.
Set the Power Buttons option to Shut Down and press the Power On/Off pushbutton.

The Restart command

The Restart command in the Shut Down window and the Task Manager's Shut Down menu instructs Windows to perform a systematic shutdown and then immediately restart the computer. There's one important difference between a hard boot from the On/Off pushbutton or the reset pushbutton and a soft reboot with a Restart command: when you use a Windows command to restart the computer, the BIOS does not reset a marker in memory that tells another part of the BIOS to run the complete Power-On Self Test (POST). As a result, the overall startup time on a soft reboot can be up to a minute or two faster than a hard reboot.

If nothing else works …

In the unlikely event that you can't shut down your computer with Ctrl+Alt+Delete or the reset pushbutton, there's one more thing you can do that should always work: pull the plug. It might seem obvious right now, but in a panic situation when there's smoke coming out of the power supply and nothing else responds, it's more important to cut your losses and turn everything off than to worry about a systematic shutdown.

If possible, pull the plug out of the computer's rear panel first so you don't pull out some other cord by mistake, but if it's easier to reach the wall outlet, go ahead and pull that one before you try to move the computer or other furniture to get to the back of the computer.