It seems like your OS or hard drive is not being detected by the computer, it could be a failing hard drive or you just corrupted the OS somehow. Try reinstalling Mac OS X, if you still have the recovery disk to your mac just insert it into your mac while its on and then reboot. As soon as the chime happens which is that sound when you turn on your mac that bahhh sound, hold the key C for about 10 seconds and then let go wait a couple of minutes while your mac boots into the disk. Afterwards click ok to the front screen and click Utility which is on the top menu bar and open Disk Utility, click your Macintosh HD partition and click the erase tab which is on the right box of where information about your hard drive is located and then click erase after its done erasing exit disk utility and proceed to install your OS. If your hard drive wasnt shown in disk utility then you need a new hard drive because then that means its dead.