Check SQL Agent Properties in Management studio and verify error log location. We had this problem after failed drive when the path wasn't set on the new drive.
It is a rights issue. I have added the user under which the agent runs as a local admin and it worked. Best answer will be to see exactly what kind of rights it needs.
If this event occurs after starting the SQL server:
1. Check the error log file at C:\Program Files\Microsoft SQL Server\<instance_folder>\MSSQL\LOG.
2. Using SQL Server Management Studio, connect to the server and try to start the SQL agent. If the SQL agent indicates "agent XPs disabled", there is a configuration error or service account issue that is preventing SQL agent from running.
A. Run the following to re-enable SQL agent:
sp_configure "show advanced options", 1;
sp_configure "Agent XPs", 1;
B. Do not attempt to start SQL Agent yet. Resolve the SQL Agent issue before starting SQL Agent.
You can use SQL Server Configuration Manager to check the SQL Agent service account. Make sure it is set to an account that has proper permissions. This was the cause in my case.