Yeah, 4.3 is quite old, there have been a lot of changes since then:
Did you disable also all modifications? I forgot to mention this in my reply above.
Maybe, maybe not. Depending on what is broken, the page could be throwing some kind of PHP error or exception. If that is what's happening, the page won't load at all. For example the template might be calling a function that has been removed or changed in 4.7. Considering you upgraded from 4.3 it's certainly possible.