Knowledge Base TNS -->ORA-12560: TNS:protocol adapter error

When starting up the database it raised  following  error;

SQL> conn sys as sysdba
Enter password:
ERROR:
ORA-12560: TNS:protocol adapter error

for this I set my ORACLE_SID to the particular database id to this

In the command prompt (cmd) type this  (fin is my database name)
C:\Users\Dell>set ORACLE_SID=FIN  

Now its working fine :)

• make sure 11g passwords are case sensitive.

---------------------------------------------------------------------------------------------------
C:\Users\Dell>SQLPLUS SYS AS SYSDBA

SQL*Plus: Release 11.2.0.3.0 Production on Sun Feb 9 17:37:49 2014

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Enter password:

Connected to:
Oracle Database 11g Release 11.2.0.3.0 - Production

SQL> STARTUP
ORA-01081: cannot start already-running ORACLE - shut it down first