Bigger hard drive or format and start all over again. Make sure you backup first.
How I can Start the back up?
You can also see if it will boot into Safe Mode.
Press the power button - as soon as you hear the chime, press the shift key and hold it until you see the Apple on screen - it can take a couple of minutes to boot.
Yep. Wanna is spelt 'want to'. And havva read of these:-