"Please enter passphrase for disk"

Solution 1:

If your root partition is not encrypted, or if you're not sure, try this: Boot off a Ubuntu install DVD or USB stick and select Try Ubuntu.

If you are able to see your files, edit /etc/fstab and remove the line that looks like this:

/dev/mapper/ubuntu--vg-swap_1 none            swap    sw              0       0

Reboot and it shouldn't ask you for a passphrase.

If you can't see any files then your root partition is encrypted. I personally haven't experienced this issue, so I can't speak with certainty, but the system shouldn't need to access the swap partition to boot... try pushing enter a few times and see if it gives up and continues booting.