Hi PAVB,
I did set ORACLE_SID and ORACLE_HOME and connected to the instance. But still I can't start the DB.

C:\>set oracle_sid=gtdb

C:\>set oracle_home=e:\oracle

C:\>sqlplus /nolog

SQL*Plus: Release 9.2.0.1.0 - Production on Fri Oct 12 16:36:56 2007

Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.

SQL> conn sys as sysdba;
Enter password:
Connected to an idle instance.
SQL> startup force
ORA-01031: insufficient privileges
SQL>

And also, it is not generating any UDUMP or BDUMP logs in its folders. What could be other possible reason for it to not allow me to start the DB?

Thanks,