Stuck at boot after "cryptsetup: set up successfully"

Do you know how to chroot into it from a live USB stick with Trisquel on it?

I'll put the steps here in case they help. Also it will be something I can find here later for myself:

1. Download Trisquel and make a live USB stick using your favorite method
2. Boot up with the live USB stick on the broken computer, boot into the live environment, become root:
sudo -i
3. Determine your disk layout (do these steps logged in as root unless otherwise specified):
fdisk -l
You should get some output showing what the partitions are on your laptop hard drive, like /dev/sdb1 being your boot partition, /dev/sdb2 being your root partition, etc. You should also get some output showing what partition your live USB is on, such as /dev/sda1. For purposes of this walk-through, I'll say that /dev/sdb1 is the laptop's boot partition, /dev/sdb2 is the laptop's root partition, and /dev/sda1 is the USB stick's root partition.

4. Make a directory on the Live USB stick to mount the laptop hard drive onto:
mkdir /mnt/laptop

5. Mount the laptop partitions onto the Live USB stick:
mount /dev/sdb2 /mnt/laptop
mount /dev/sdb1 /mnt/laptop/boot
Note - if you don't have a separate /boot/ partition on your laptop hard drive, then you would skip the step of mounting the /boot/ partition.

6. Now mount some folders from the USB stick that contain device files we will need when we chroot into the laptop:
mount -t proc /proc /mnt/laptop/proc
mount -o bind /sys /mnt/laptop/sys
mount -o bind /dev /mnt/laptop/dev
mount --make-rslave /mnt/laptop/sys
mount --make-rslave /mnt/laptop/dev

7. mount the pseudo terminals so you can use apt to update or install software in the chroot environment:

mount -o bind /dev/pts /mnt/laptop/dev/pts

8. Normally Trisquel is probably running on /dev/sda when your laptop is working, but here we are mounting the laptop hard drive (as seen from the USB stick) as /dev/sdb. Now let's redirect it so that when we are in the chroot, we see the laptop hard drive as /dev/sda like it wants to see it:
mount -o bind /dev/sdb /mnt/laptop/dev/sda

NOTE - the above may be reverse for you, since you mentioned in your post that the hard drive seemed to be booting as /dev/sdb1. If that's the case, you may just want to tell the chroot that the /dev/sdb is really /dev/sdb. I tried this on my Trisquel install and it did not hurt:
mount -o bind /dev/sdb /mnt/laptop/dev/sdbOnly do that if your laptop hard drive is NOT showing up as /dev/sda when it's running itself in the laptop.

9. chroot into the laptop now:
chroot /mnt/laptop
You may get a warning message about bin/bash. Keep going.

10. You'll be logged into the chroot environment as root. Now, get the source right for your path environment variables:
source /etc/environment

11. Check to see that from within the chroot that you really are looking at the laptop hard drive as /dev/sda:
fdisk -l /dev/sda
Hopefully you'll get some output saying that /dev/sda1 is the boot sector, /dev/sda2 is the linux root filesystem, and so forth.

Note - in your case you might be checking to see if the laptop hard drive is listed as /dev/sdb:
fdiskk -l /dev/sdb

12. Try to update the system on the laptop hard drive:
apt update
apt upgrade

Let us know any trouble you have inside the chroot, such as lack of network access.

While inside the chroot you can look for other things to fix, besides just updating your software.

13. When finished, exit out of the chroot back to the USB stick, make yourself root again, and unmount everything:
exit
sudo -i
umount -f /mnt/laptop

14. Shut down, remove the USB stick, and see if you can boot your laptop now:
halt

Edit: my unmount command from step 13 was incorrect - fixed it