when far enough away from us are not visible...whether you want to consider that star dark or not is up to you.Edit - Brown dwarves and neutron stars, while labeled such do not exhibit the characteristics assigned to stars.......
There are however stars which burn at less intense temperatures, the lowest intensity stars, when far enough away from us are not visible...whether you want to consider that star "dark" or not is up to you.
Edit - Brown dwarves and neutron stars, while labeled such do not exhibit the characteristics assigned to stars. They are essentially the same things as black holes, they simply were not massive enough during their star phase to become a black hole.
Yes, "white dwarfs" and "neutron stars" eventually cool down and become black, but are still stars.
However, such stars probably don't exist now, because the time it takes them to cool down is much longer than the current age of the Universe.
If you exclude black holes, no, not yet. The Universe isn't old enough, yet. Yes, they CAN exist.