MacBook Pro - Login and startup problem

Hello everybody!

I have a MacBook pro late 2011 and I haven't had any problems until now.

Last week I downloaded OS X El Capitan and for a couple af days it worked without any problems.

One day it stopped logging in with my user. Once I typed my password, it couldn't log in and it didn't get past the loading screen which stayed on for hours until I shut down the Mac.

I tried re-installing El Capitan with Utility Disk but the problem got worse since the Mac doesn't even start up. Once I turn it on it appears the Apple logo and below it a charging bar that remanis continuosly empty.

I've tried them all and I hope that somebody who experienced my same problem and solved it can help me.

Thanks a lot in advance for your help.