undo tablespace Corrupt

Hi gurus out there

I was trying to resatrt my database after a power failure last night and I could not start it and I found this message in my alert log.I have tried to rename the DBF file and recover it but nothing works. Can you please tell me what to do .I have a full database export from ast week.

Errors in file d:\ltpp_database\imsprod\trace\imsprod_ora_2128.tr c:
ORA-01578: ORACLE data block corrupted (file # 2, block # 89)
ORA-01110: data file 2: 'D:\LTPP_DATABASE\IMSPROD\TABLESPACES\UNDO02.DBF'

Tue Jul 27 14:19:45 2004
Error 1578 happened during db open, shutting down database
USER: terminating instance due to error 1578
Tue Jul 27 14:19:47 2004
Errors in file d:\ltpp_database\imsprod\trace\imsprod_pmon_2100.t rc:
ORA-01578: ORACLE data block corrupted (file # , block # )

Instance terminated by USER, pid = 2128
ORA-1092 signalled during: alter database open.