Google this page is not a duplicate
How to turn on your computer (Buying a Computer, Part 6)
Press this button for about one second and then let go.
If your operating system is Windows XP, first the black and white screen will display some text and detect devices, then the windows XP screen will appear and log the main user onto the computer. If any of the devices have not been connected to the computer before, it may automatically attempt to install the new devices and may also request that you insert the required compact disks, which normally come with the device into the compact disk drive.
When only one user has been set up on the computer it will connect (log on) to this user if no password is set. If a password has been set or there is more than one user, a list of users is displayed.
Click the small picture (ICON) next to the user which is to be connected and if required enter the supplied password. IP