It's probably a busted drive. I would try holding down the option key while booting, and see if your drive appears.
Try booting into reconvery from a pendrive/CD (make it using a friend's mac, or another mac of your own. Some public libraries will have macs, mine does). Repair permissions, repair the disk, and then click the apple logo in the status bar in recovery. Click the option pertaining to the selection of the boot volume of the computer, and select your internal drive (usually Macintosh HD) and then try booting again.
If that doesn't work, take out your hard drive and mount it externally, and try booting with option.
If nothing has worked, your drive is broken, and you need to take it to a computer place to get it fixed. If you have a solid state (which I doubt because of your OS version not supporting TRIM), your drive is probably messed up and is not fixable (this is a problem with SandForce SSDs)