Over time your computer will accumulate inconsistencies and corruptions, this happens as a result of normal operation.  Just the automatic or self updating of software to a later version may cause this as there are so many permutations of software installation and hardware components that no manufacturer can possibly test that their product is not unintentionally interfering with all others.  This is exacerbated by installing new programs, and running malicious code - viruses or malware.

Usually these corruptions will not cause inconvenience, but their effect is often cumulative and eventually unexpected behaviour or degrading performance will trigger a call for help.  Many individual problems can be resolved but the time, and therefore cost, of repairing a computer that has not been maintained for several years is often more than that of starting again from scratch.

The benefit of deleting all data from the hard disk drive and installing Windows again is that all problems are quickly resolved.  But there is a penalty: all programs that were in use would need to be installed again.  This means that the installation CD or download location must be to hand as well as any activation codes or product keys necessary to make the software work.

The first step must be to take a backup copy of what you have currently.  That way, if something goes wrong, you can never get into a worse state than the present.  Your backup copy must be on a medium other than the disk you will be reinstalling Windows on and written using a program that will be available to you when a restoration is required.  Some backup options are:

• An image copy. (recommended) This would involve copying the entire disk so that it can be put back with no further actions in case it was needed.  Individual files can usually be extracted as well.

• Use the File and Transfer Wizard that comes with Windows XP or Windows Easy Transfer with later versions of Windows.  This has the advantage of enabling you to save settings as well as files and is fairly automated.  However, it would restore unwanted settings as well as the ‘good’ ones.

• Regular file backups.  Here, you copy just the photos, documents, music, e-mail, address book and favourites that are in your account and any others (such as the shared area).  It would not allow you to recover from an unbootable disk.

Once you have a backup, you should test it to satisfy yourself that it is a sound copy that can be relied on in a worst case scenario.

Next you should ensure that the BIOS is set to boot off the optical drive in preference to the hard disk drive.  Make sure you have assembled all you will need: the Windows installation disk, the latest drivers downloaded from the hardware manufacturers' websites for the motherboard and any other peripherals you have, your backup and the means to access it, the backup installation media, all other programs (e.g. Microsoft Office) and any serial numbers or activation codes required.

Now you can load the Windows CD in the optical drive and boot off it.  You will need to delete all partitions off the disk first, then format it (not using the ‘quick’ option) and follow the Windows reinstallation steps.  You may like to research what is necessary before taking the plunge.  Websites such as 

http://support.microsoft.com/kb/978788 or

http://www.theeldergeek.com/clean_installation_of_windows_xp.htm  or 

http://www.pcworld.com/article/129977/how_to_reinstall_windows_xp.html  may be helpful here.

Once Windows is installed, you must install the video, chipset, network and motherboard drivers at the minimum and in the appropriate sequence.  Now I suggest installing an Internet Security Suite before physically connecting to the Internet.  Having done that the next step must be to update the anti-virus product and then visit the Microsoft Update website and install the latest service pack and any later patches.  I recommend not taking driver updates from Microsoft, but visiting the manufacturers’ own sites for the necessary software.

Now you are ready to install any programs you want on your computer, and finally copy back your personal photos, documents, music, e-mail, address book and favourites that are in your account and any others (such as the shared area).

This procedure is possibly lengthy, but it almost guarantees a faster and less error prone computer at the end and may prolong the useful life of your computer.