With every new install on windows xp, an account named Administrator is created, this account is created automatically and has no password. So what you have to do? Well, if you haven't changed the password to this account, then you can restart your computer and reboot it in Safe Mode, pressing F8 on the setup screen, before the windows xp boot screen load. Then you choose the option, Boot in Safe Mode, if the Administrator account has no password (by default it doesn't) you'll now login to your windows xp account, once you do that, go to Control Panel, User Accounts and change the password you had on the your personal account to something you'll not forget this time. In short, you'll use the default account administrator to login into your personal account "Your Name" and change the password using the Administrator account. After changing your password, you reboot and log into your personal account with the password you chose. :-)

If you have changed the password of your personal Windows XP account, and you don't remember to what you did change the password to, and that's the reason why you cannot log into your account anymore.
You can use System Restore to restore your computer to a point where you did know your password, right before you change it. By default windows create Recover Points, to use this method you'll have to use our previously "Safe Mode" boot, in which you press F8 repeatedly on the BIOS screen. Once you are on the desktop, you click in Start>All Programs>Accessories>System Tools>System Restore. And choose a recover point date in which you were with your old password, click in restore.

If you couldn't get back your account with those two steps above, or if your account on Windows XP is by default named Administrator and not your username, then you'll have to use some softwares to get back your password or reset the password on your windows xp.

In this module I'll be explaining how to reset your password using the Microsoft tool called "Password Reset Disk".
To acesses this tool you will reboot your computer normally, click over your username, and then press Enter, then you'll be prompted with an error message:

"Did you forget your password? You can click the "?" button to see your password hint. Or you can use your password reset disk. Please type your password again. Be sure to use the correct uppercase and lowercase letters."

You're going to click on "Use your password reset disk".
In the Password Reset Wizard dialog box, click Next.
Insert the Password Reset Disk into your drive and click Next.
Type a new password and then confirm your new password.
Type a new password hint, choose one that will really help you to remember.
Now click finish and try to log in on your windows xp using your username and your new password.