Recover Database Probelm

Dear All

I take online whole database backup and when i restore

startup mount;

ORACLE instance started.

Total System Global Area 8925478912 bytes

Fixed Size                  2085656 bytes

Variable Size            4445965544 bytes

Database Buffers         4462739456 bytes

Redo Buffers               14688256 bytes

Database mounted.

SQL> alter database open resetlogs;

alter database open resetlogs

*

ERROR at line 1:

ORA-01113: file 1 needs media recovery

ORA-01110: data file 1: '/oracle/ARP/sapdata1/system_1/system.data1'

please say how i solved this problem

Nainesh