tns protocol error

I have two different databases
orcl123 and company
I cannot connect company database
it shows error
This is the what is happening when I connect two diffent database.
set oracle_sid=orcl123
SQL> conn / as sysdba
Connected to an idle instance.
SQL> startup mount
ORACLE instance started.

Total System Global Area  535662592 bytes                                      
Fixed Size                  1334380 bytes                                      
Variable Size             255853460 bytes                                      
Database Buffers          272629760 bytes                                      
Redo Buffers                5844992 bytes                                      
Database mounted.
SQL> alter database open;

Database altered.

SQL> select name from v$database;

NAME                                                                            
---------                                                                      
ORCL123                                                                        

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> spool off

set oracle_sid=company
sqlplus /nolog
SQL> conn / as sysdba
ERROR:
ORA-12560: TNS:protocol adapter error

Could you please help me why company database could not connect.
My oracle version is oracle 11g.
Thanks in advance