frazzled is correct, you are seeing this because the password for the 'RSC\Administrator' has changed. Go into services, double click sql server agent and change the password to what the new password is. If you do not need the agent to access network drives I'd suggest having it log on as the local system account. Otherwise create a domain user with lower privilages than the administrator account.
BTW, This is a pervasive forum, not a Sql Server forum.
You may solve this problem by assigning user rights to the user: "NT AUTHORITY\SYSTEM".
Follow these steps:
Open "SQL Server Management Studio".
Open "Security, and then Logins".
Rightclick on user: "NT AUTHORITY\SYSTEM >> Properties".
Select "Server Roles" tab, and check the "sysadmin" server role.
You are done. SQL Server Agent will be started now.