Q: Grey screen, apple logo and spinning wheel

Downloaded it and then I hit the restart button, then I went for an hour and found the screen black.

So, I tried to turn it on, and a grey screen showed with apple logo and a spinning wheel :(

For the record, I already updated another laptop to Mavricks and it works perfectly!

I don't know what's wrong, I tried to turn it on more the once and it's the same result.