this common error in windows, and you can be occur for more than one reason and you need to check them all to make sure you did everything is right, the error prevent the oracle services to start automatically and if you check

ORADIM.LOG….
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C:\Oracle\Ora11g\bin\oradim.exe -startup -sid ptdb -usrpwd * -log oradim.log -nocheck 0
Thu Nov 15 15:16:15 2012
ORA-01031: insufficient privileges

You have to check :

1- startup type for the services ( if it’s set automatically )
2- Group to user ( the user should be in ORA_DBA Group )
3 – you can check log on tab in the service properties and set the username and password who responsible about this services and can do it by:

Go to Control Panel -> Administrative Tools -> Services .

Choose oracle services and then
click “properties”. Select the “Log On” tab and note the account that is set to run the service.

Thank you
Osama mustafa