upgrading from 14.04 to 15.10 - cannot boot (doesn't have required/sbin/init)

I tried to upgrade my machine from 14.04 to 15.10 but now бm getting:

Target filesystem doesn't have required /sbin/init.
/bin/sh: 0: can't open ro
[     2.388786] kernel panic - not syncing: Attempt to kill init!

i tried booting in sevrel option from the advance setting but with не luck...

what should i do?