When you get to the login screen, you could try to use Ctrl-Alt-F1 and then Ctrl-Alt-F7. Make sure your caps lock is off, and see if you notice a response while you type in your password.
Otherwise, you may want to verify your download using an MD5 checksum, and then re-installing. I don't know what version of Linux Lite you're attempting to log into, and I've not seen this before in any version. But troubleshooting this may take longer than just reinstalling. If you created a separate /home partition, you can reinstall without having to restore your backup, and your Thunderbird settings should still be intact.
