DBCC CHECKDB consistency-based I/O error
Ensure you have a valid backup; hopefully it will be from prior to the corruption, but not so long ago that the data isn't useful. You should set this aside in case direct repair isn't possible and you need to recover data from the backup.
The documentation explains what to do to correct the problem - you can try the REPAIR_REBUILD option, and if that doesn't solve it, you can move on to next steps according to the guy who wrote CHECKDB, Paul Randal. He has a ton of articles on CHECKDB, that cover just about every conceivable scenario, but which ones are relevant to you will depend on what happens next when you attempt your repair. One that may be useful as a start, so you know which table you'll need to fix:


Finding a table name from a page ID