How to remove this error..?

SQL> connect internal;
Connected.
SQL> select name from v$database;

NAME
---------
AAAA

SQL> shutdown abort
ORACLE instance shut down.
SQL> startup open;
ORACLE instance started.

Total System Global Area 86657052 bytes
Fixed Size 75804 bytes
Variable Size 56520704 bytes
Database Buffers 29982720 bytes
Redo Buffers 77824 bytes
ORA-01990: error opening password file 'C:\oracle\ora81\DATABASE\PWDaaaa.ORA'

Thanks
Harry