Resolving Resource Conflicts
Any time two or more devices are assigned the same resource without being managed by Windows' IRQ sharing, there is a resource conflict. If the devices attempt to access the same resource at the same time, a lockup is likely to occur. Lockups are situations in which the computer suddenly stops responding. The first sign of this is usually that the mouse pointer won't move. You'll also notice that the cursors stop blinking, and keys depressed on the keyboard have no effect. These symptoms can sometimes happen temporarily, however, so there is an easy test to determine if the computer is really locked up (as long as your keyboard has a working Num Lock or Caps Lock light): press the or key on the keyboard. If the light doesn't go on or off, you can bet that your computer is locked up. If the Num Lock light responds, wait a minute or two to see if the computer starts responding again, and then try the Num Lock test again. If the computer is truly locked up, the only alternative is to shut off the power to the computer and reboot. You can shut off the power on all newer computers (those with a soft power switch) by pressing and holding the power switch for several seconds until the power goes off. A soft power switch is one that activates an electronic circuit to start or stop the computer, as opposed to a mechanical switch that simply shuts power on and off by opening or closing the circuit. On computers with mechanical switches, simply pressing the button once will do the trick. Many computers have a mechanical power supply switch on the back that can be used. If all else fails, turn off the surge suppressor/power strip switch, or pull out the plug.Reconnect the power, if disconnected, and restart the computer. To avoid another lockup, go into Safe Mode. Safe Mode is a mode of Windows in which only essential hardware is activated. This will allow you to resolve many problems with a greatly reduced risk of the computer locking up in the middle of your efforts. Follow the instructions in Tutorial 2.5b as applicable to boot into Safe Mode.
 
Tutorial 2.5b: Booting into Safe Mode in Windows 2000 and XP After restarting power, watch for a black screen with the message "Starting Windows." Underneath will be a message that says, "For troubleshooting and advanced startup options for Windows ____, press F8." You'll have to press in the few seconds that the message appears. Once the progress bar starts, it is too late and you'll have to press + + as described in Tutorial 2.5a to restart and try again. Some configurations cause systems not to show any of these messages. In this case, repeatedly press as soon as it starts to boot. Figure 2.15 shows the Windows Startup menu.
 
Assuming you can successfully boot into Safe Mode, you can then open Device Manager and attempt to resolve the resource conflict. If you can't even boot into Safe Mode, see Chapter 11 for troubleshooting information. You can manually assign resources through Device Manager, but it's generally better to let Windows make resource assignments if possible. If you have legacy expansion cards that work only on one IRQ, or cards that have jumpers or DIP switches to select between only two IRQs, you'll have to do a bit of planning to resolve the conflict. Make the selection to view devices by resource in Device Manager. In 9x, select My Computer in the Device Manager Window and click the Properties button below. Then, make sure the Interrupt Request (IRQ) option button is selected. In 2000 and XP, click "Resources by type" in the View menu. This displays a list of IRQs and the devices assigned to them. Then, make a note (literally—write it down on paper) of all devices in which a yellow exclamation point indicates a problem. By double-clicking each of these devices and then the Resources tab on the dialog box that appears, you'll see which resources the device is using, and a list of conflicts on the bottom of the dialog box. If you don't see the resources used, click the Manual configuration button and the conflict list should appear. Write down all this information. Then, review the list of IRQs for unused numbers, noting that there are certain IRQs that are reserved and cannot be reassigned, and that some devices must have certain IRQs and I/O addresses and can accept no others. Then, write down a list of problem devices and plan for them to use free IRQs and I/O addresses. Configure manually in the Resources tab of the device's Properties dialog box by clearing the "Use automatic settings" check box, highlighting the Resource type in the Resource settings windows, and clicking the Change Setting button, as shown in Figure 2.16. Note that many devices will not let you change settings, and often the Automatic settings check box is dimmed (grayed out).  

Figure 2.16: Changing resources manually.
 
Tip If you can't seem to get the resource conflict solved, check in the BIOS to make sure that PnP is enabled. Sometimes, PnP can be shut off spontaneously.
 
As you can see, there aren't many other available IRQs, and some of the ones not listed might be taken by other devices. If you have taken an A+ course, you probably know that the COM port resource assignments are almost set in stone. However, there are not many devices that use COM ports 1 through 4 these days. Internal modems use internal COM ports, which we discuss in Chapter 8. Certain PDAs, UPSs, and external modems use COM ports, but some of these devices also use USB or other interfaces. Therefore, unless the user has and needs multiple COM ports, they could be disabled in Device Manager or in the BIOS, freeing up their resources. Some machines have multiple parallel (LPT) ports. These are good for many printers and scanners; however, most or all parallel port scanners have pass-throughs allowing you to connect the scanner to the computer's parallel port and a printer to the scanner's pass-through parallel port, while using only one IRQ. Therefore, unless the user needs more than one parallel port, additional LPT ports can be disabled as well. Of course, if there is no IRQ shortage or problem with resource conflicts, it is best to leave the configuration as is. In other words, if it ain't broke, don't fix it.
 
If you still have resource conflicts, you can remove (uninstall) all Plug and Play devices with conflicts and reboot the computer. Depending on the Windows version, you might be asked to reboot after each device is recognized and reinstalled. Reboot as soon as you are prompted. You might have to try many different configurations until you eliminate all the conflicts.