How to login as Administrator in Windows XP?

How many of us ever realized that the Administrator account is one of the best way to get back your computer in shape.This built-in Administrator account is hidden from Welcome Screen when a user account with Administrator privileges exists and enabled.
This Administrator account is mainly for the purpose to have a look on what is inside the computer. Normally, in a troubleshoting process it is very useful, for example in a case where you can't launch any kind of application if you are login with your account.

In Windows XP Home Edition, you can login as built-in Administrator in Safe Mode only. For XP Professional, press CTRL + ALT + DEL twice at the Welcome Screen and input your Administrator password in the classic logon window that appears.