With data corruption, the internal structure of the database is inconsistent. Data corruption is usually caused by a hardware failure or an anomaly in the Oracle software. This will manifest itself in any number of Oracle error messages. Most likely you will be able to identify the actual database block that is corrupt. Your options for recovery depend on the kind of information stored in that location:
You should be able to salvage rows from blocks that are not corrupt by copying them over to another table and then dropping the table. It may be necessary to exclude rows using unique keys or ROWIDs. Alternately, you may have to perform datafile or database recovery.
You will have to either recover the SYSTEM tablespace using media recovery or recreate the database and recover using full, cumulative, and incremental exports.
If there are uncommitted transactions, you will have to perform datafile or tablespace recovery.