I always have this same problem with Trisquel 8 encryption.
When the screen comes up you have to hit ALT CTRL Delete to reboot the computer which should boot into the screen for Advanced options and choose a older kernel.
It really depends the computer. First you should try the ALT CTRL Delete and log into your current kernel as that is how I boot into Trisquel encryption for Trisquel 8.
If that fails than try an older kernel.
