macbook does not start after upgrade to el capitan

After receiving the update available message for El Capitan 10.11.1 I started the download.

My MacBook would have supposed to restart on its own, which it didn't.

Then it was stuck forever.

I tried restarting with Coammand+ALT and R and P keys, then downloaded El Capitan again.

Same thing, the Mac wouldn't get on its feet.

Today I tried Shift-Start: same thing: the starting bar is filling up for over an hour and then just stops.

Is there anything else I could try ?

No, I do not have a timemachine backup.

thanks.