It sounds like your drive may be failing. Can you boot to Recovery HD and Verify Disk?
I think you may have clicked it twice it normally ends with appears to be OK. Is that a MAcBook with a removable battery?
Yes I meant "easily" removed sorry...ok
1. Shut down the computer. 2. Plug in the power adapter to a power source, connecting it to the Mac if its not already connected. 3. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time. 4. Release all the keys and the power button at the same time. 5. Press the power button to turn on the computer. 6. Press and hold the Command-Option-P-R keys before the gray screen appears. 7. Hold the keys down until the computer restarts again at least twice. 8. Release the keys and immediately hold down the ‘Command’ + R’ keys on the keyboard during the start up process. When you see the Apple Logo you can let go.
When the machine boots you may have to choose your language then you will see the OS X Utilities screen. Select the Disk Utility and then select Continue. Then in Disk Utility select Macintosh HD in the left column (if there are two with that name or it is named something else choose the first indented item) select the First Aid tab if it is not already selected, then click on Verify Disk on the far right. If that is ok quit Disk Utility and select Reinstall Mac OS X.