The error message "ORA-27101 Shared memory realm does not exist." is often generated when trying to start a new database, even those which have been created by the Oracle Installer software.
The first thing i would do is check your oracle sid, also that the Oracle services are running on the WIN server. Then check your net8 settings especially your tnsnames.ora file is it correct. Have you got multiple Oracle Homes, If you do not use other Oracle homes try to get rid from the unused.
Is your current Oracle home the Home where your instance resides?
