The Java version can upgrade automatically if you have it set that way. And that certainly could impact how things work on Ancestry or other sites that might use java applets (I haven't used Ancestry.com, so I don't know for sure, but it's a good possibility they do use Java applets). The current Java version is version 8, so that really makes sense with your original post.

If that's the case, there may be some messed up security settings now for the ancestry.com site. What they can do is go to:
Control Panel>Programs>Java

That will pop up a dialog window. Click on the security tab, and then the Edit Site List button. Add "https://ancestry.com" to the exceptions list, and it might solve it for you.

That's what I would try first. If that doesn't work, you can downgrade your java by going here: http://www.oracle.com/technetwork/java/archive-139210.html

But, probably before doing that, I would call up Ancestry and see what they suggest. My bet is the security thing will take care of it for you, and it won't hurt at all to do that.