SQL DBA : Unable to Start SQL Server Agent (Agent XP is disabled )

I got this error after Windows server reboot .

Route Causes :

1.Check the SQL Server Agent running status from SQL Server configuration manager .
2. Password might be changed due to company security policies.

3. The SQL Server Agent service security principal (SID) is removed or missing from the SQL Server 2008 installation.
4. Check if MSDB rebuild recently.

Possible Solutions :

1. Changes the SQL Server Agent services statues to Automatic instead of Manual.

2. Provide the updated password to SQL Server Agent services account.

3.   You can follow the below mentioned procedure for SID fix.

  1.      Click Start, point to All Programs, point to Microsoft SQL Server 2008, and then click SQL Server Management Studio.

2.      In the Connect to Server dialog box, verify the default settings, and then click Connect.

3.      In Object Explorer, right-click the server, and then click New Query to open a new Database Engine Query Editor window.

4.      In the Query Editor window, type the following Transact-SQL statement.

EXEC sp_addsrvrolemember '<Domain>\<Account>', 'sysadmin';

5.      Note <Domain> represents the domain name, and <Account> represents the domain user account that is assigned to the SQL Server 2008 Agent service.

6.      Press F5 to execute the query.

7.      Close the SQL Server Management Studio window.

8.      Try to restart the SQL Server Agent service.

4. If "MSDB" database rebuild recently then execute the below scripts

sp_configure 'show advanced options', 1;

RECONFIGURE;

sp_configure 'Agent XPs', 0;

RECONFIGURE;