SQL Server Agent will not start

Believe this problem is because I had SQL Server 2008 on my machine and then added SQL Server 2008 R2. Today I had renamed the old MSSQL10 directories with a zz at front to mark them as old. Then SQL Server Agent did not start.
First I had:
Error message when you use SQL Server Configuration Manager to restart the SQL Server Agent service in SQL Server 2008:
“The request failed or the service did not respond in a timely fashion”
http://support.microsoft.com/kb/955494
Suggested using Start > Administrative Tools > Services or Services.msc and start from there.

This led to next problem
The SQL Server Agent (MSSQLSERVER) service on Local Computer started and then stopped.  Some services stop automatically if they have no work to do, for example, the Performance Logs and Alerts service.
http://blogs.msdn.com/b/sqlserverfaq/archive/2009/06/12/unable-to-start-sql-server-agent.aspx
Found that the registry entry
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL.1\SQLServerAgent
ErrorLogFile key was pointing at a location which was 2008 not 2008 R2
Chnaged the key value and SQL Server Agent started OK

SOLVED