I found the 'fix' in the end. Somehow the booting drivers cache was obsolete (or corrupt). This cache is created by the command: kextcache. I guess that was the reason the macbook booted after about 1 hour of resting. I executed $ sudo kextcache -i / and it worked like a charm. Issue fixed!
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First, disconnect any external disk you may have to prevent erasing the incorrect disk.. In recovery mode (Command+Option+R), there is an option Utilities->Terminal which opens a command line. First get the number of your disk with # diskutil list you'll see something like /dev/disk0 /dev/disk1 ... Do not confuse your internal physical disk with the disk image the Recovery process mounts. You will know which one is the right one because of the size (256 GB, 512 GB, etc). The disk image is only 2 GB size. Let's say in your case is '0' de number. Then you run the formating process #diskutil eraseDisk JHFS+ DiskName /dev/disk0 You can choose different file systems. It does not matter because after showing on the diskutil GUI next time you can re-format to any format. 'DiskName' is only a label. You can choose whatever you want. JHFS+ is Journaled HFS Plus File System I suggest googling 'diskutil eraseDisk' to get more info in order to feel comfortable about the process. Good luck!
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