Can't log in after 16.04 upgrade

[erikamit]

I am a beginner Ubuntu user. Yesterday, I unfortunately downloaded and installed the upgrade to 16.04. When tried to start my computer this morning (an aging HP laptop), Ubuntu gave me a brand new log in screen that I've never seen before. I entered my password, and just got the same login screen again. I have searched around the internet and found all sorts of suggestions, but none of them worked. Now I can't use my laptop because I can't get beyond the login screen. Is there any way to get back to a previous Ubuntu installation so that I can actually use my laptop again?

[erikamit]

No one had any suggestions. I guess I will have to pop the hard drive out, delete the operating system, then reinstall. My Ubuntu installation files are 2 years old. Is there an archive somewhere of old Ubuntu updates so that I can get to a version that works? Because I clearly can't use 16.04.