Run DBCC CHECKDB.
The output will tell you what is corrupted. If you're lucky, it's a nonclustered index. You can drop it and recreate it and walk away a winner. If it's any other type of data storage, you'll need to go to your last good backup.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning