I believe all the questions are correct. The first and third sentences are making a statement of what HAS happened, e.g. I fell down yesterday.
In the second and last sentence 'frozen' is describing the state that John and the people died in, that is- how they were found and in this case, they were FROZEN, e.g. when I FOUND the bike,it was broken.
Finally, the fourth sentence is describing what is still happening presently for example, I am walking.