You want to manually add a new hardware component because Windows did not recognize it, or Windows found your new hardware but previously installed hardware disappeared.
Using the BIOS
Press the appropriate key(s) to access the built-in BIOS setup program. Typically, pressing the DEL or F2 key will access setup, although some systems use F1, F10, Ctrl+Alt+S, or ESC.
Locate the selection for Reset NVRAM, Reset ESCD, or Reset Plug and Play.
Select Yes or Reset.
Save the settings and restart your PC.
Using a graphical user interface
Right-click My Computer.
Select the Hardware tab.
Click the Device Manager button.
Right-click the computer icon at the top of the list.
Select Scan for hardware changes.
If the Device Manager finds new devices it will automatically locate and install drivers or prompt you for the location of suitable driver files. Device Manager may also find devices that conflict with others and display the yellow exclamation point icon alerting you to problems that need further investigation, covered in Recipes Recipe 3.2 and Recipe 3.7.
Using a command-line interface
Download DEVCON from http://support.microsoft.com/default.aspx?scid=kb;EN-US;Q311272, then uncompress and save the files to a known location on your hard drive C:\DEVCON seems like a friendly location.
Go to Start, select Run, then type in CMD and click OK.
In the command prompt window navigate to the folder DEVCON is stored in C:\DEVCON\i386 for most of us.
Type in the following command to force Windows to re-evaluate the system for new devices:
> devcon rescan
Type in the following command to all of the devices Windows knows about:
> devcon findall *
Scroll through the command-prompt window to see whether your devices have been discovered.
Occasionally, a slow or conflicted Plug and Play device may not be immediately or automatically recognized or reconfigured by the BIOS upon booting, or by Windows' hardware detection. Detection failure could be caused by a Plug and Play device not responding to new discovery by the BIOS, or by one of the devices being unable to use an alternative available interface. Also, Windows may not be able to address a new device because it is busy with other tasks and misses the new device notification from the Hardware Abstraction Layer. Resetting Plug and Play enumeration in the BIOS or telling Windows' Device Manager to "look again" using Device Manager's scan process or DEVCON to tell Windows to re-eunumerate devices should fix this problem.
Microsoft's web sites provide considerable information toward getting Plug and Play and Windows to cooperate. Check out the details at www.microsoft.com/resources/documentation/Windows/XP/all/reskit/en-us/prdh_dmt_pjoy.asp and www.microsoft.com/windowsxp/using/setup/learnmore/devicemgr.mspx.