How to reinstall windows xp if files are missing??

CLEAN INSTALLATION

NOTE: Before proceeding, make sure all necessary backups are completed.

* Insert the Windows XP Reinstallation CD into the top CD drive
* Remove any external devices from the computer: (except the mouse & keyboard) printer, scanner, camera, joystick
* Configure your computer to boot to the top CD\DVD\CD-R -RW\DVD+R +RW drive

- Restart the system
- When the logo screen appears, press the [F2] key to enter the System Setup program
- Press the [Down Arrow] key on your keyboard to highlight Boot Sequence
- [press Enter] to display the available boot devices
- Press the [Up Arrow] key or the [Down Arrow] key to highlight IDE CD-ROM Device
- Press the [plus +] key or the [minus -] key on the keyboard to move IDE CD-ROM Device to the TOP of the list
- Press the [ESC] key
- Press the [ESC] key to Save Changes and Exit
- When you are prompted to Save changes and exit now, [press Enter]

* Your system will now boot to the Windows XP CD that you had inserted into the CD drive
* The following message appears: Press any key to boot from the CD
* Press the [Spacebar] to boot to the Windows XP CD. The Windows XP Setup screen appears
* [press Enter]to setup Windows. The Windows XP Licensing Agreement screen appears
* Press the [F8] key to accept the license agreement. The partitioning screen appears
* If the hard drive is already partitioned (this is most common), [press Enter]to continue.
* If the hard drive partitions are not listed or detected, you will need to create a partition on the hard drive. Press the [C] key and then follow the on-screen prompts to create a partition. If you are unsure which settings to select, you may want to use the default selections that are displayed

* If your hard drive already contains a copy of a Windows operating system, a Caution screen appears. Press the [C] key to continue. The format options screen appears:
- Format the partition using the NTFS file system (Quick)
- Format the partition using the FAT file system (Quick)
- Format the partition using the NTFS file system
- Format the partition using the FAT file system
- Leave the current file system in place (no changes)
* Dell recommends that you select the first option since that is how we shipped it from the factory
* Choose "Format the partition using the NTFS file system (Quick)", then [press Enter]. The Caution screen appears if you select to format the hard drive
* Press the [F] key to format the hard drive. The setup program will now copy files to your system. This will take several minutes, please wait. After the files have been copied, a message appears and notifies you that the computer will be restarted
* Press the [Enter] key to restart the computer or a timer will count down and restart the computer automatically
* When the computer restarts, the following message appears: Press any key to boot from the CD. Do NOT press any keys!!!
* The Windows XP Setup window appears. Many devices will be detected during this process. This will take several minutes, please wait
* Once this process is completed, the Regional and Language Options window appears
* Click Next
* The Personalize Your Software window appears.
* In the Name: field, type your name. Optionally, you may type your organization's name into the Organization: field
* Click Next
* If you are installing Windows XP Home Edition, the "What's your computer's name" window appears
* Click Next to accept the default selections
* If you are installing Windows XP Professional: The Computer Name and Administrator Password window appears
* Type a name for this computer in the Computer Name: field (or you may accept the default). Type a password in the Administrator Password: field and then type the same password in the Confirm Password: field. Click Next to continue.
NOTE: If you have a modem installed in your computer, you may be prompted to type the area code for your location.
* The Date and Time Settings window appears. Click to select the appropriate time zone for your location from the Time Zone field
* Click Next
* Depending upon your network configuration, you may be prompted for additional information regarding your network card (such as the domain name and workgroup name). If you are unsure of these settings, contact your Network Administrator or accept the default selections. After all hardware has been detected and the files have been copied to the hard drive, the system will restart. When the computer restarts, the following message appears: Press any key to boot from the CD. Do NOT press any keys!!!
* Once the Desktop appears, eject/remove the black Operating System Reinstallation CD from the top CD\DVD\CD-R -RW\DVD+R +RW drive
* You may be prompted for user information. Type the name of any additional users that will be using the computer
* Click Next to continue

After installing the operating system, you need to install the drivers and software for the system.

actually you can reinstall your xp system but this you can't, why:

the reason
your windows xp system are being updated every month...
the version from original system are being extracted to a new version....

by this time reformat you hard disk...