One of the Security Features of Windows is requiring users to enter credentials to log on to their PC.
If a user account automatically logs on, anyone who has physical access to the computer can restart it and access the user’s files.There are lots of time when automatic logon might be preferred in a scenario such as when computer is physically secure and need quick access to PC. To configure PC to automatically log on follow following steps;

Note: This can only be perform in standalone PC (Workgroup PC), this cannot be perform in a PC connected to domain.

Step I- Click Start, type netplwiz, and then press Enter.

Step II- In the User Accounts dialog box, click the account you want to automatically log on to. If it is available, clear the Users Must Enter A User Name And Password To Use This Computer check box and click OK.

Step III-  In the Automatically Log On dialog box, enter the user’s password twice. Click OK. The next time you restart the computer, it will automatically log on with the local user account you selected.

Note: Configuring automatic logon stores the user’s password in the registry unencrypted, where someone might be able to retrieve it.