The best way would be to try and do a repair but for that you will need a XP disc
If you do have your Windows CD
To start the Recovery Console directly from the Windows XP CD you would do the following:
Insert the Windows XP cd in your computer. Restart your computer so you are booting off of the CD. When the Welcome to Setup screen appears, press the R button on your keyboard to start the Recovery Console. The Recovery Console will start and ask you which Windows installation you would like to log on to. If you have multiple Windows installations, it will list each one, and you would enter the number associated with the installation you would like to work on and press enter. If you have just one Windows installation, type 1 and press enter. It will then prompt you for the Administrator's password. If there is no password, simply press enter. Otherwise type in the password and then press enter. If you entered the correct password you will now be presented with a C:\Windows> prompt and you can start using the Recovery Console.
Easy to follow instructions here enter link description here