Oracle Startup issue

Hi Team,

When I am trying to start the database I am getting the bellow error

SQL> startup mount
ORACLE instance started.

Total System Global Area  146010632 bytes
Fixed Size                   737800 bytes
Variable Size             138412032 bytes
Database Buffers            6553600 bytes
Redo Buffers                 307200 bytes
Database mounted.
SQL> alter database open;
alter database open
*
ERROR at line 1:
ORA-01122: database file 1 failed verification check
ORA-01110: data file 1: '/dev/vg_ora_sd01/rlvsdsys1'
ORA-01251: Unknown File Header Version read for file number 1

Oracle DB version is :- 9.2.0.6.0

OS version is :- HP Unix.

could anybody help on the above mentioned Issue

Thanks

Manoj