<p>I just forgot the password. Can anyone help me how to get back the password.</p>

There is no way to get the old password back. Log into the SQL server management console as a machine or domain admin using integrated authentication, you can then change any password (including sa).
Start the SQL service again and use the new created login (recovery in my example)
Go via the security panel to the properties and change the password of the SA account.
Now write down the new SA password.