My late 2011 macbook pro (purchased early 2012), running El Capitan - wouldn't boot up so I tried http://goo.gl/G4YbWq with mixed success. I would go through the different steps and sometimes it would reboot and sometimes it wouldn't but there was no pattern to which step worked - computer would run ok for 1-2 hours sometimes even longer and then freeze. Although now I'm back to the white screen with horizontal lines through the logo and nothing works.

What I've done:
re-installed El Capitan
checked the disk and all appears to OK
re-installed from time machine - this was a mild disaster, everything backed up ie apps etc but my documents didn't!

I called apple but my extended warranty expired early last year, they suggested a couple of agents; connect nz, imagetext, yoobee, urbertech etc - up until now I've managed to overcome any issues my macbook through up at me but this time I'm snookered (could be the logic board). 

Would appreciate any advice on either overcoming problem or a good repair agent.

Many thanks,

Maurice