Why is there no life on planets such as Pluto, Neptune, or Venus?

In our solar system, Earth is the only planet on which life has so been discovered. The other planets of the solar system do not have the same conditions as those on Earth. The major factors that determine whether a planet can have life forms include temperature, the presence of water and atmosphere, and the others.
The planets such as Mercury and Venus are very close to the Sun and hence are too hot to sustain life. At high temperatures, water evaporates resulting in loss of water. Venus has an atmosphere that contains 96% carbon dioxide, an average surface temperature of 735 K, and atmospheric pressure which is 92 times that of Earth—therefore, it is incapable of supporting life.
Planets such as Neptune and Pluto (it is no longer a planet as of 2006!) are too far away from the Sun and, hence, too cold to support life. Neptune has a high concentration of hydrogen and helium in its atmosphere, making it unsuitable for Earth-like life forms.
Thus, distance from Sun is one of the major factors deciding whether life can exist on a planet or not. There are other factors, such as presence of liquid water, suitable atmosphere, the presence of a solid surface, as well.
Hope this helps.