This can happen to any of us, usually we forget Windows accounts' passwords, when we want it least of all. But such situations are very common and this is good when you know how to reset it, as it will save your time and efforts in future.

This is an instruction how to reset account password in Windows XP (on condition that you do not have password set on Administrator account):

1. Reboot PC/laptop in Safe Mode (press and hold 'F8' button when the PC starts and choose 'Safe Mode' in the list). Log in under 'Administrator' account.

Frequently this account doesn't have password set. 

You're prompted to set password on it during Windows XP installation.

2. Go to [Start] > [Control Panel] > [Administrative Tools] > [Computer Management] :

3. Expend 'System Tools' node, then 'Local Users & Groups' and choose 'Users'. On the right side choose user account and right-click on it. Menu with options will appear.

Select "Set Password..." option.

4. The confirmation window will appear. Press 'Proceed' button to continue the process of resetting password:

5. After that the window with the passwords fields will appear. Enter new password twice, or leave these fields empty to log in without password.