Sierra upgrade, boot disk disappear

[TheBook]

Hi,

I downloaded Sierra on my MacBook Retina. But the installation stops at 40%. When I want to select a boot disk, there is none. At Disk Utility Macintosh HD is light grey and I can't activate the disk. I did a test by pressing D when turning on the computer but that stops and crashes at the last little bit as well.

Any Idea what to do?

Thanks.

 

[jbarley]

I know what I would do if in your position, but that would only help if you made a total backup before you started the upgrade.

 

[TheBook]

That's good because I already made a back up before installing Sierra