Enable SQL Agent using SP_Config

Some time if we start the SQL server Agent service but sql server agent is not started so that time we can use the sp_configure option to start the agent. 
  1. EXEC SP_CONFIGURE 'Agent XPs'  
After execute this if you got the error then execute the below command 
  1. EXEC SP_CONFIGURE 'show advanced options',1  
  2. GO  
  3. RECONFIGURE  
  4. GO  
  5. EXEC SP_CONFIGURE 'show advanced options'  
And then run the command again:
  1. EXEC SP_CONFIGURE 'Agent XPs',1  
  2. GO  
  3. RECONFIGURE