To start with you should make a full back up of anything important before doing anything else.
Your drive has a corruption so you'll need to boot your system on an external HD or USB thumb drive that has a working system. Then you can run Disk Utility to fix the drive. Depending on what you encounter you may need to repartition & format the entire drive. I would strongly recommend running the disk test services so any bad blocks are isolated out.
As an option you might think about getting a more comprehensive disk utility like Drive Genius as it also can defragment your drive as well (a common cause of system slow down).