SQL Agent Service not starting after SQL 2008 Upgrade

Root Cause
The service control was looking to old path , for example when you run the sc config, you can locate that its not in mssql10.dev1

C:\>sc \\GANESHJ qc sqlagent$dev1

[SC] GetServiceConfig SUCCESS
SERVICE_NAME : sqlagent$dev1
TYPE : 10 WIN32_OWN_PROCESS
START_TYPE : 2 AUTO_START
ERROR_CONTROL : 1 NORMAL
BINARY_PATH_NAME : C:\Program Files\Microsoft SQL Server\MSSQL$DEV1\binn\sqlagent.exe -i DEV1
LOAD_ORDER_GROUP : TAG : 0
DISPLAY_NAME : SQLAgent$DEV1
DEPENDENCIES : MSSQL$DEV1
SERVICE_START_NAME : .\svcganeshj

But the same has to be as below: "C:\Program Files\Microsoft SQL Server\MSSQL10.DEV1\MSSQL\Binn\SQLAGENT.EXE" -i DEV1

Fix
To fix, navigate in registry to and modify the same to correct value Hklm\system\currentcontrolset\services\sqlagent$prdpos and modify the same to correct value as above.